Fluorine-containing aromatic compound

Abstract: Disclosed is a fluorine-containing aromatic compound represented by the formula: wherein: each of R 1 and R 2 independently represents a hydrogen atom or a C 1 -C 19 alkyl group, wherein the total number of carbon atoms in R 1 and R 2 is from 4 to 19; and each R f is an unsubstituted or partially substituted C 1 -C 25 fluorocarbon group in which the ratio of fluorine atom or atoms to carbon atom or atoms is from 0.6 to 3. The compound of the present invention has various excellent properties, such as very high miscibility with hydrocarbons and low bioaccumulation (or low bioconcentration), so that is can be advantageously used not only as lubricant oils for refrigeration equipment using HFC refrigerants or an additive in a refrigerant system using in combination an HFC refrigerant and a hydrocarbon lubricant, but also as lubricants for general purpose, or additives or modifiers for various types of oily substances and polymeric materials.

Description: BACKGROUND OF THE INVENTION Field Of The Invention The present invention relates to a fluorine-containing aromatic compound. More particularly, the present invention is concerned with a fluorine-containing aromatic compound having a specific molecular structure, which has various excellent properties, such as very high miscibility with hydrocarbons and low bioaccumulation (or low bioconcentration), so that it can be advantageously used not only as lubricant oils for refrigeration equipment using hydrofluorocarbon refrigerants (hereinafter frequently referred to simply as "HFC refrigerants") or an additive in a refrigerant system using in combination an HFC refrigerant and a hydrocarbon lubricant, but also as lubricants for general purpose, or additives or modifiers for various types of oily substances and polymeric materials. Discussion Of Related Art CFC-12 is still currently, widely used as a refrigerant in refrigeration equipment for car air conditioners and refrigerators, while HCFC-22 is widely used as a refrigerant in refrigeration equipment for room air conditioners. However, development of a refrigerant which can be used in substitution for chlorine-containing refrigerants, such as CFC-12 and HCFC-22, has been desired from the viewpoint of the protection of the ozone layer. As substitute refrigerants, the above-mentioned lower hydrofluorocarbons having 1 to 5 carbon atoms are promising. Of these, hydrofluorocarbons having 1 to 2 carbon atoms are particularly preferred. In conventional refrigeration systems using CFC-12 or HCFC-22, mineral oil or alkylbenzene is used as a lubricant for a compressor of the refrigeration system. CFC-12 and HCFC-22 exhibit high oleophilicity since they contain chlorine atoms, so that they are miscible with mineral oil and alkylbenzene over a wide temperature range. Accordingly, even in the refrigeration systems where evaporation and condensation of the refrigerant are repeated, phase separation of CFC-12 or HCFC-22 as the refrigerant from the lubricant does not occur. However, various types of hydrofluorocarbon refrigerants (hereinafter frequently referred to simply as "HFC refrigerants") and HFE refrigerants are not satisfactorily miscible with hydrocarbon compounds, such as mineral oil and alkylbenzene, since such refrigerants contain no chlorine atom. Therefore, when a hydrocarbon compound, such as mineral oil or alkylbenzene, is used as a lubricant, various serious problems occur. For example, because the lubricant is replaced by the refrigerant in a compressor, the lubrication becomes unsatisfactory. And the lubricant adheres to the inner wall of the heat exchanger, leading to a lowering of the heat exchange efficiency. A lubricant for use in refrigeration equipment employing, as a refrigerant, a hydrofluorocarbon (HFC) such as HFC-134a, and a hydrofluoroether (HFE), should be miscible with either HFC or HFE at least over a temperature range from 0 °C to 50 °C, preferably over a range from -20 °C to 70 °C, more preferably over a range from -40 °C to 90 °C, and most preferably over a still wider temperature range. Various polyalkylene glycol compounds, polyol ester compounds and polycarbonate compounds have been proposed as lubricants highly miscible with hydrofluorocarbons, such as HFC-134a, for use in combination with such hydrofluorocarbons. For example, polyalkylene glycols having at least two hydroxyl groups (especially, polyoxypropylene glycol) disclosed in the specification of U.S. Patent No.4,755,316, are described as exhibiting a good miscibility with hydrofluorocarbons, such as HFC-134a, over a wide temperature range. However, the temperature range over which polyalkylene glycols are miscible with HFC-134a is still unsatisfactory for their functioning as lubricants, and improvement of the miscibility, especially at high temperatures, is required. Polyoxalkylene glycols have not only unsatisfactory lubricating properties under application conditions, but also high moisture absorption (or water absorption) properties. Therefore, various problems are likely to arise, such as corrosion of metals, and lowering of a volume resistivity (a lowering of a volume resistivity causes a problem in the case of a closed type refrigeration equipment, such as a refrigerator.) Accordingly, polyoxyalkylene glycols are not good lubricants for a refrigeration system from a practical point of view. Polyol ester compounds, disclosed in Japanese Patent Application Laid-Open Specification Nos. 3-128991 and 3-179091 and polycarbonate compounds in Nos.5-32688 and 5-86391, are generally considered to be also highly miscible with HFC-134a. However, since such compounds exhibit high moisture absorption properties due to the polar groups contained therein, a problem in durability in terms of hydrolysis resistance is caused. In addition to the above-mentioned polyalkylene glycol and polyol ester oils, fluorine-containing oils are considered to be lubricants miscible with fluoroalkanes, such as HFC-134a. With respect to the fluorine-containing oils, the following patent application publications are noted. In Japanese Patent Application Laid-Open Specification No. 60-96684, it is taught that when a fluoro-lubricant oil, such as a fluorinated silicone or a perfluoropolyether, is used in a fluorocarbon working medium for a heat pump or the like, the heat resistance of the fluorocarbon working medium is improved. However, no description is made therein with respect to the miscibility of the lubricant oil with a hydrofluoroalkane to be used as a working medium. Japanese Patent Application Laid-open Specification No. 1-118598 describes the use of fluorocompounds, such as a perfluoropolyether and a fluorinated silicone, as a lubricant for fluorocarbon refrigerants. However, no description is made therein with respect to the miscibility of such fluorocompounds with a hydrofluoroalkane at low temperatures below room temperature. Further, no description is made therein with respect to the miscibility of fluorocompounds, other than a perfluoropolyether and a fluorinated silicone, with a hydrofluoroalkane. The present inventors previously examined the miscibilities of perfluoropolyethers having various structures indicated below, inclusive of perfluoropolyethers (trade name: Fomblin Y-06, Y-25 and Y-45, manufactured and sold by Nippon Montedison Co., Ltd., Japan) employed in Examples of Japanese Patent Application Laid-Open Specification Nos. 60-96684 and 1-118598, with a fluoroalkane, such as HFC-134a, HFC-134 and HFC-152a. wherein each of q 1 , q 2 , q 3 , q 4 , q 5 and q 6 is a positive integer. As a result, it was found that there were cases where miscibilities were observed at temperatures as high as about room temperature or more, but in any case, miscibilities were unsatisfactory at low temperatures. Accordingly, it was confirmed that such perfluoropolyethers were not suitable as a lubricant for use in refrigeration equipment employing a fluoroalkane, such as HFC-134a, HFC-134 and HFC-152a, as a refrigerant. Moreover, because such perfluoropolyethers are not miscible with various types of hydrocarbon oils, such as alkylbenzene and mineral oil, the perfluoropolyethers cannot also be used in the form of a mixed lubricant thereof with the above-mentioned hydrocarbon oils, for use in refrigeration equipment employing a hydrofluorocarbon refrigerant. On the other hand, in EP 0 528 043 A1, it is described that the fluorine-containing aromatic compound represented by formula R(XR f ) n , the definition of which is substantially the same as that of formula (A) hereof, exhibits excellent miscibility with HFC refrigerants, while exhibiting desirable characteristics, such as satisfactory heat resistance, lubricating properties and durability. It is also described therein to the effect that the compound of formula R(XR f ) n can be used in the form of mixtures with other oils; that the other lubricant oil usable in combination with the above compound is generally selected from those miscible with a fluoroalkane refrigerant to a certain degree, and more particularly, the other lubricant oil is selected from the group consisting of perfluoropolyether oils, perfluoropolyether oils having a carbonyl-containing group, such as a carboxyl group, a carboxylate group, an amido group, a ketone group and an ester group, or having a polar group, such as a hydroxyl group, an amino group, an imido group, an ether group, a benzoimidazol group, a phosphite group, a phosphine group, a nitrile group, a phosphotriazine group and a triazine group, chlorofluorocarbon oils, polyalkylene glycol oils, ester oils and fluorinated silicone oils; and that appropriate types of oils are selected from these oils, taking into consideration the miscibility thereof with the compound R(XR f ) n and the viscosity and lubrication characteristics of the resultant lubricating composition. However, in EP 0 528 043 A1, there is no description with respect the miscibility of these mixtures (mixed oils) with HFC refrigerants. In these situations, the present inventors have made extensive and intensive studies with a view toward further improving the properties of the lubricant having the structure disclosed in EP 0 528 043 A1 in order to provide a practically further improved lubricant exhibiting not only excellent miscibility with HFC refrigerants, such as HFC-134a, and HFE refrigerants over a wide temperature range, but also satisfying all requirements of properties for use thereof as a lubricant in refrigeration equipment, that is, low temperature fluidity, low moisture absorption properties, high electrical insulation, prolonged durability, excellent lubricating properties, high safety, such as low bioaccumulation (bioconcentration), and low cost. As a result, it has surprisingly, unexpectedly been found that a fluorine-containing aromatic compound having a specific molecular structure represented by the formula (C-1) mentioned below has various excellent properties, such as very high miscibility with hydrocarbons and low bioaccumulation (or low bioconcentration), so that it can be advantageously used not only as lubricant oils for refrigeration equipment using HFC refrigerants or an additive in a refrigerant system using in combination an HFC refrigerant and a hydrocarbon lubricant, but also as lubricants for general purpose, or additives or modifiers for various types of oily substances and polymeric materials. wherein: each of R 1 and R 2 independently represents a hydrogen atom or an alkyl group having from 1 to 19 carbon atoms, wherein the total number of carbon atoms in R 1 and R 2 is from 4 to 19; and each R f is an unsubstituted or partially substituted fluorocarbon group having from 1 to 25 carbon atoms in which the ratio of fluorine atom or atoms to carbon atom or atoms is from 0.6 to 3, wherein the unsubstituted fluorocarbon group is selected from the group consisting of a fluoroalkyl group, a fluoroalkenyl group, a fluoroaryl group, a fluoroalkylaryl group and a fluoroaralkyl group, in which each of the alkyl, alkenyl, aryl, alkylaryl and aralkyl groups is partially or entirely substituted with at least one fluorine atom, and the partially substituted fluorocarbon group has at least one substituent other than fluorine and hydrogen atoms in an amount such that the ratio of the at least one substituent to the total number of fluorine and hydrogen atoms of the partially substituted fluorocarbon group is not greater than 1.5, and wherein a main chain of the unsubstituted or partially substituted fluorocarbon group optionally has from 1 to 7 ether linkages; wherein the R f groups are the same or different. The present invention has been completed, based on such novel findings. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a fluorine-containing aromatic compound represented by the formula: wherein: each of R 1 and R 2 independently represents a hydrogen atom or an alkyl group having from 1 to 19 carbon atoms, wherein the total number of carbon atoms in R 1 and R 2 is from 4 to 19; and each R f is an unsubstituted or partially substituted fluorocarbon group having from 1 to 25 carbon atoms in which the ratio of fluorine atom or atoms to carbon atom or atoms is from 0.6 to 3, wherein the unsubstituted fluorocarbon group is selected from the group consisting of a fluoroalkyl group, a fluoroalkenyl group, a fluoroaryl group, a fluoroalkylaryl and a fluoroaralkyl group, in which each of the alkyl, alkenyl, aryl, alkylaryl and aralkyl groups is partially or entirely substituted with at least one fluorine atom, and the partially substituted fluorocarbon group has at least one substituent other than fluorine and hydrogen atoms in an amount such that the ratio of the at least one substituent to the total number of fluorine and hydrogen atoms of the partially substituted fluorocarbon group is not greater than 1.5, and wherein a main chain of the unsubstituted or partially substituted fluorocarbon group optionally has from 1 to 7 ether linkages; wherein the R f groups are the same or different. The foregoing and other objects, features and advantages of the present invention will become apparent from the following detailed description and appended claims, taken in connection with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: Fig. 1 is a chart showing the infrared spectrum of fluorine-containing aromatic compound [S3][compound (C-1)] prepared in Referential Example 3. DETAILED DESCRIPTION OF THE INVENTION According to one aspect of the present invention, there is provided a fluorine-containing aromatic compound represented by the formula: wherein: each of R 1 and R 2 independently represents a hydrogen atom or an alkyl group having from 1 to 19 carbon atoms, wherein the total number of carbon atoms in R 1 and R 2 is from 4 to 19; and each R f is an unsubstituted or partially substituted fluorocarbon group having from 1 to 25 carbon atoms in which the ratio of fluorine atom or atoms to carbon atom or atoms is from 0.6 to 3, wherein the unsubstituted fluorocarbon group is selected from the group consisting of a fluoroalkyl group, a fluoroalkenyl group, a fluoroaryl group, a fluoroalkylaryl and a fluoroaralkyl group, in which each of the alkyl, alkenyl, aryl, alkylaryl and aralkyl groups is partially or entirely substituted with at least one fluorine atom, and the partially substituted fluorocarbon group has at least one substituent other than fluorine and hydrogen atoms in an amount such that the ratio of the at least one substituent to the total number of fluorine and hydrogen atoms of the partially substituted fluorocarbon group is not greater than 1.5, and wherein a main chain of the unsubstituted or partially substituted fluorocarbon group optionally has from 1 to 7 ether linkages; wherein the R f groups are the same or different. With respect to the compound (C-1) of the present invention, it is particularly advantageous to use the compound (C-1) in a lubricant oil composition comprising: (A) the compound (C-1); and (B) an alkyl- or alkyl derivative-substituted aromatic compound comprising at least one substituted aromatic nucleus selected from the group consisting of a substituted benzene nucleus and a substituted naphthalene nucleus, wherein a substituent of the at least one substituted aromatic nucleus is an unsubstituted or substituted alkyl group having from 1 to 30 carbon atoms, or a derivative thereof, the alkyl- or alkyl derivative-substituted aromatic compound (B) having a kinetic viscosity of from 0.1 to 500 cSt as measured at 40 °C, the lubricant oil composition having a kinetic viscosity of from 2 to 500 cSt as measured at 40 °C. The alkyl- or alkyl derivative-substituted aromatic compound (B) is cheap, but has excellent properties, such as low temperature fluidity, low moisture absorption properties, and high electrical insulation. However, such a compound (B) has a problem in that although it is miscible with hydrofluorocarbons to some extent, the miscibility exhibited thereby is still not sufficient for it to be advantageously used as a lubricant for refrigeration equipment using hydrofluorocarbon (HFC) and hydrofluoroether (HFE) refrigerants. In addition, the compound (B) has another problem in that it inherently exhibits unsatisfactory lubricating properties. However, it has unexpectedly been found that the alkyl- or alkyl derivative-substituted aromatic compound (B) exhibits excellent miscibility with the fluorine-containing aromatic compound (C-1) and that the resultant lubricant oil composition obtained by mixing compound (C-1) with compound (B) exhibits miscibility with HFC refrigerants, such as HFC-134a and HFC-32, and HFE refrigerants and, therefore, can be advantageously used as a lubricant for refrigeration equipment. Further, it is noted that, in the above lubricant oil composition, the lubricating properties of aromatic compound (B) itself can also be remarkably improved. More surprisingly, it has also been found that the lubricant oil composition can synergistically exhibit more excellent lubricating properties than any of the fluorine-containing aromatic compound (C-1) alone and the alkyl- or alkyl derivative-substituted aromatic compound (B) alone, which are components of the lubricant oil composition. Further, it should be noted that when the fluorine-containing aromatic compound (C-1) is used alone as a lubricant for refrigerants, it is unsatisfactory with respect to the desired low temperature fluidity, low moisture absorption properties and high electrical insulation, however, these properties can be remarkably improved by mixing the fluorine-containing aromatic compound (C-1) with the alkyl- or alkyl derivative-substituted aromatic compound (B). Furthermore, it should be noted that, by changing the amount of the alkyl- or alkyl derivative-substituted aromatic compound (B) to be added to the fluorine-containing aromatic compound (C-1), the degree of dissolution of hydrofluorocarbon refrigerant in the refrigeration composition [composed of a refrigerant and a mixture of compound (C-1) and (B)] can be regulated, so that the viscosity and lubricating properties of the resultant refrigerant composition can be controlled. Thus, it has advantageously become possible to provide lubricant oil compositions suitably adapted for various types of refrigeration systems. As mentioned above, when the fluorine-containing aromatic compound (C-1) is mixed with the alkyl- or alkyl derivative-substituted aromatic (B), respective drawbacks inevitably accompanying the compound (C-1) and the compound (B) can be eliminated, so that an excellent lubricant oil composition can be provided, which can simultaneously satisfy all requirements of properties for use thereof as a lubricant in the refrigeration system employing HFC and HFE refrigerants, such as excellent miscibility with HFC and HFE refrigerants, satisfactory low temperature fluidity, low moisture absorption properties, high electrical insulation, and durability. This is an unexpected synergistic effect of the present invention, which has not been achieved by the use of compound (C-1) alone or compound (B) alone. The reasons why the compound (C-1) has excellent miscibility with a variety of HFC refrigerants (eg., HFC-134a) and HFE refrigerants, have not yet been clearly elucidated. However, the following reasons can be presumed. Each of HFC and HFE refrigerants has at least one C-F bond and at least one C-H bond, and, hence, it is believed to have a hybrid structure formed of a fluorocarbon group and a hydrocarbon group. Therefore, it can be understood that the fluorocarbon group of such a refrigerant exhibits affinity to conventional perfluorinated oils (e.g., a perfluoropolyether), whereas the hydrocarbon group thereof does not exhibit affinity to the perfluorinated oil at all. On the other hand, it has been known that HFC refrigerants, such as HFC-134a, exhibit a miscibility with a perfluorinated polyether to some extent, but the miscibility is unsatisfactory in a low temperature range. This is believed to be due to the fact that the HFC refrigerant has a hydrocarbon group which has low affinity to the perfluorinated polyether. In a fluorine-containing compound represented by the formula: R(XR f ) n wherein X represents an oxygen or a sulfur atom; n is an integer of from 1 to 4; R represents an n-valent aromatic group; and R f is as defined for formula (C-1), the aromatic group R comprising at least one aromatic nucleus is linked to a fluorocarbon group R f through an oxygen or a sulfur atom. The aromatic group R in formula (A) has affinity to a hydrocarbon group of HFC and HFE refrigerants, whereas the fluorocarbon group R f in formula (A) has affinity to a fluorocarbon group of such refrigerants. Thus, the fluorine-containing aromatic compound (A) has affinity to both of the fluorocarbon group and hydrocarbon group of HFC and HFE refrigerants, so that the fluorine-containing compound (A) exhibits excellent miscibility with such refrigerants over a wide temperature range. In this connection, it should be noted that the fluorocarbon group R f in the fluorine-containing aromatic compound (A) plays an important role in the achievement of miscibility of the compound (A) with HFC or HFE refrigerant. This can be understood from the following experimental facts. Compounds, respectively, represented by formula (1-1) wherein R f is -CF 2 CF 2 H and by formula (1-2) wherein R f is -CF 2 H exhibit miscibility with HFC-134a at from -78 °C to 90 °C, whereas a compound represented by formula (1-0) wherein -CH 2 CH 2 (containing no fluorine atom) is used instead of R f does not exhibit miscibility with HFC-134a at temperature in the range from room temperature to 90 °C. It was found by the present inventors for the first time that the compound (A) comprising the R group and the R f group exhibits a satisfactory miscibility with HFC and HFE refrigerants having a hybrid structure formed of a fluorocarbon group and a hydrocarbon group. Since R in formula (A) is a group containing at least one aromatic nucleus, the compound (A) exhibits high stability, as compared to a compound in which the R group in formula (A) is replaced with a saturated alicyclic or a saturated aliphatic hydrocarbon group. The reason for this has not yet been elucidated, however, it is believed to reside in that a R-X-R f bond is stable when R is a group containing at least one aromatic nucleus, as compared to the case where R is replaced with a saturated alicyclic or a saturated aliphatic hydrocarbon group. The mechanism of an achievement of miscibility between the HFC and HFE refrigerants and the lubricant oil composition comprising in combination the fluorine-containing aromatic compound (A) and the alkyl- or alkyl derivative-substituted aromatic compound (B) has not yet been elucidated, but is believed to be as follows. As mentioned above, the fluorine-containing aromatic compound (A) exhibits excellent miscibility with HFC and HFE refrigerants. On the other hand, it has been found that the fluorine-containing aromatic compound (A) exhibits excellent miscibility with various types of the alkyl- or alkyl derivative-substituted aromatic compounds (B) to be used in the present invention. That is, the fluorine-containing aromatic compound (A) has amphiphilic characteristics such that it exhibits excellent miscibility not only with HFC and HFE refrigerants, but also with the alkyl- or alkyl derivative-substituted aromatic compound (B). Therefore, in the refrigerant composition comprising the above-mentioned three components, namely (1) the fluorine-containing aromatic compound (A), (2) the alkyl- or alkyl derivative-substituted aromatic compound (B), and (3) HFC and/or HFE refrigerant, the fluorine-containing aromatic compound (A) is believed to serve as a miscibility agent for the alkyl- or alkyl derivative-substituted aromatic compound (B) and the HFC and/or HFE refrigerant. The present inventors have found that, of the above-mentioned fluorine-containing aromatic compounds (A), a compound represented by formula (C-1), which is the compound of the present invention, has especially high miscibility with the alkyl- or alkyl derivative-substituted aromatic compound (B). Further, it should be noted that the miscibility of the fluorine-containing aromatic compound (C-1) with HFC and HFE refrigerants is not adversely affected even by mixing thereof with a large amount of the alkyl- or alkyl derivative-substituted aromatic compound (B). Therefore, the lubricant oil composition comprising the fluorine-containing aromatic compound of formula (C-1) and the alkyl- or alkyl derivative-substituted aromatic compound (B) has especially excellent properties, such as low temperature fluidity, low moisture absorption properties and high electrical insulation. Furthermore, since the fluorine-containing aromatic compound represented by formula (C-1) exhibits an extremely excellent miscibility with hydrocarbons, such compounds can be advantageously used as an additive in a refrigerant system using in combination an HFC refrigerant and a hydrocarbon lubricant, such as alkylbenzene or mineral oil (which is well-known to be unsatisfactory in miscibility with the HFC refrigerant), so that the oil return properties can be remarkably improved. Another notable feature of the fluorine-containing compound represented by formula (C-1) resides in that the compounds exhibit low bioaccumulation (or low bioconcentration), so that these compounds can be safely used. By virtue of the above-mentioned excellent properties of the fluorine-containing compound represented by formula (C-1), this compound (even if used alone) is also advantageously useful not only as lubricant oils for refrigeration equipment using HFC refrigerants but also as lubricants for general purpose, or additives or modifiers for various types of oily substances and polymeric materials. Hereinbelow, the present invention will be described in more detail. The above mentioned partially substituted fluorocarbon group as R f has at least one substituent other than fluorine and hydrogen atoms. The main chain of the unsubstituted or partially substituted fluorocarbon group may optionally have at least one ether linkage therein. When the main chain includes at least one ether linkage, the number of the ether linkages is from 1 to 7, preferably from 1 to 3. In addition, as R f , the unsubstituted or partially substituted fluorocarbon group or its derivative group having at least one ether linkage therein may be substituted with other substituent. When the R f contains a substituent other than a fluorine atom and an ether linkage, the number of such substituents is generally from 1 to 4, preferably from 1 to 2, more preferably 1. As such a substituent, there is no particular limitation as long as the fluorine-containing aromatic compound (C-1) is stable during the use in a refrigerator. However, the following examples of substituents can be mentioned: (1) a halogen atom, exclusive of a fluorine atom, i.e., a chlorine atom, a bromine atom and an iodine atom. Of these, a chlorine atom is preferred; (2) an active hydrogen-containing monovalent group selected from the group consisting of a hydroxyl group, an amino group and a thiol group, with the proviso that the active hydrogen-containing group is not bonded to the carbon atom having a halogen atom bonded thereto; and (3) a monovalent group having from 1 to 10 carbon atoms, preferably from 1 to 6 carbon atoms, more preferably from 1 to 3 carbon atoms, and selected from the group consisting of a thioalkoxy group, an aikyl-substituted amino group, an acyl group, an acyloxy group, a carboalkoxy group, a nitrile group, an amido group and an imido group, which are optionally substituted with at least one fluorine atom. The ratio of the at least one substituent to the total number of fluorine and hydrogen atoms of the partially substituted fluorocarbon group is not greater than 1.5, preferably not greater than 1.0. Of these partially substituted fluorocarbon groups mentioned above, ether linkage-containing fluorocarbon groups and chlorine-containing fluorocarbon groups are preferred because not only is excellent stability exhibited but also synthesis is easy. In R f , the ratio of fluorine atom to carbon atom is-generally from 0.6 to 3, preferably from 1 to 3, and more preferably from 1.5 to 3. When the ratio of fluorine atom to carbon atom in R f is too low, unfavorably, the compound of formula (C-1) is likely to exhibit poor miscibility with hydrofluorocarbons or fluorine-containing ether refrigerants and exhibit poor stability. The number of carbon atoms in R f is generally in the range of from 1 to 25, preferably from 1 to 10, and more preferably from 1 to 3. When the number of carbon atoms in R f is greater than 25, unfavorably, various problems arise such that it is difficult to obtain raw materials and also to synthesize a product therefrom, that synthesis and subsequent purification thereof are time-consuming, and that the viscosity of an obtained product becomes too high. As the structure of R f , there is no particular limitation as long as the above-mentioned requirements are satisfied. The representative structure of R f is shown below, but is not limited to the following structure. A preferred structure of the unsubstituted or partially substituted fluorocarbon group R f of formula (C-1) is represented by the formula: wherein: each of A 1 , A 2 and A 3 is independently a fluorine atom or a fluoroalkyl group having from 1 to 6 carbon atoms, preferably from 1 to 3 carbon atoms, more preferably a fluorine atom or -CF 3 , wherein the fluorine atom is optionally replaced with or the fluoroalkyl group is optionally substituted with at least one substituent selected from the group consisting of: (C 1 ) a halogen atom, exclusive of a fluorine atom, (C 2 ) an active hydrogen-containing monovalent group selected from the group consisting of a hydroxyl group, an amino group and a thiol group, with the proviso that the active hydrogen-containing group is not bonded to the carbon atom having a halogen atom bonded thereto, and (C 3 ) a monovalent group having from 1 to 10 carbon atoms, and selected from the group consisting of a thioalkoxy group, an alkyl-substituted amino group, an acyl group, an acyloxy group, a carboalkoxy group, a nitrile group, an amido group and an imido group, which are optionally substituted with at least one fluorine atom, each of B 1 , B 2 and B 3 is independently a hydrogen atom or an alkyl group having from 1 to 6 carbon atoms, preferably from 1 to 3 carbon atoms, more preferably a hydrogen atom or -CH 3 , wherein the hydrogen atom is optionally replaced with or the alkyl group is optionally substituted with a substituent selected from the group consisting of: (C 1 ) a halogen atom, exclusive of a fluorine atom, (C 2 ) an active hydrogen-containing monovalent group selected from the group consisting of a hydroxyl group, an amino group and a thiol group, with the proviso that the active hydrogen-containing group is not bonded to the carbon atom having a halogen atom bonded thereto, and (C 3 ) a monovalent group having from 1 to 10 carbon atoms, and selected from the group consisting of a thioalkoxy group, an alkyl-substituted amino group, an acyl group, an acyloxy group, a 5 carboalkoxy group, a nitrile group, an amido group and an imido group, which are optionally substituted with a fluorine atom, Z is a terminal group selected from the group consisting of a hydrogen atom, a fluorine atom, a phenyl group and a phenyl group substituted with an alkyl group having from 1 to 10 carbon atoms, wherein the phenyl group and substituted phenyl group are further unsubstituted or substituted with at least one fluorine atom, n 1 is an integer of from 0 to 25, and each of n 2 and n 3 is independently an integer of from 0 to 10, with the proviso that (n 1 + n 3 ) is not zero, n 4 is an integer of from 0 to 7 with the proviso that the structure of formula (A-2) satisfies the above-mentioned requirements for the fluorocarbon group R f of the compound (C-1) of the present invention. In formula (A-2), when n 1 is an integer of 2 or more, the (CA 1 A 2 ) units are the same or different, when n 2 is an integer of 2 or more, the (CB 1 B 2 ) units are the same or different, and when n 3 is an integer of 2 or more, the (CA 3 B 3 ) units are the same or different. In formula (A-2), the (CA 1 A 2 ), (CB 1 B 2 ), (CA 3 B 3 ) and (O) units may be arranged in any order, with the proviso that the (O) units are not directly linked to each other, that the (O) unit is not positioned at a terminal of formula (A-2) and not directly linked to a hydrogen atom or a fluorine atom, and that a main chain of formula (A-2) optionally contains one or two double bonds each formed, between a unit selected from (CA 1 A 2 ), (CB 1 B 2 ) and (CA 3 B 3 ) units and a neighbouring unit selected from (CA 1 A 2 ), (CA 2 B 2 ) and (CA 3 B 3 ), by a connection of A 1 -B 1 , A 1 -A 3 , B 1 -A 3 , A 2 -B 2 , A 2 -B 3 or B 2 -B 3 thereof in which each of A 1 , A 2 , A 3 , B 1 , B 2 and B 3 is a single bond. The fluorine atoms or hydrogen atoms of R f represented by formula (A-2) may be partially substituted with at least one substituent selected from the group consisting of a halogen atom exclusive of a fluorine atom, an active hydrogen-containing monovalent group and a substituent having not more than 10 carbon atoms, provided that the number of the substituents is from 1 to 4. Examples of R f groups are set out below, which are, however, only some examples of R f groups. These examples should not be construed to be limiting the present invention, and other various R f groups can be employed. Z 7 -(CF 2 ) L 1 - (CH 2 ) L 2 - wherein Z 7 represents a fluorine atom, a chlorine atom, an iodine atom or a hydrogen atom, L 1 is an integer of from 1 to 18, and L 2 is 0, 1 or 2. Specific examples of groups of formula (1) include the following groups: CF 3 -, CF 3 CH 2 -, CF 3 CH 2 CH 2 -, F-(CF 2 ) 2 -, F-(CF 2 ) 3 -, F-(CF 2 ) 6 -, F-(CF 2 ) 10 -, F-(CF 2 ) 2 - CH2 -, F-(CF 2 ) 4 -CH 2 -, F-(CF 2 ) 4 -CH 2 CH 2 -, F-(CF 2 ) 8 -CH 2 CH 2 -, I-(CF 2 ) 4 -CH 2 CH 2 -, ClCF 2 -, Cl-(CF 2 ) 2 -, Cl-(CF 2 ) 4 -, Cl(CF 2 ) 3 -CH 2 -, BrCF 2 CF 2 -, BrCF 2 -, I-CF 2 -, I-(CF 2 ) 3 -CH 2 -, H-(CF 2 ) 3 CH 2 -, H-(CF 2 ) 10 -CH 2 -, HCF 2 -, HCF 2 CH 2 CH 2 -, HCF 2 CH 2 -, and I-(CF 2 ) 2 -CH 2 CH 2 -. wherein L 2 is an integer of from 1 to 7. wherein L 2 ' is an integer of from 1 to 7, and X' represents a hydrogen atom, a chlorine atom or a bromine atom. F-(CF 2 CF 2 O) L 3 -CF 2 CH 2 - wherein L 3 is an integer of from 1 to 11. F-(CF 2 CF 2 CF 2 O) L 4 -CF 2 CF 2 CH 2 - wherein L 4 is an integer of from 1 to 7. CF 3 CHF-, CH 3 CF 2 -, CH 2 FCF 2 -, CF 2 HCF 2 -, CH 2 F-, CHF 2 CH 2 -, CF 3 CCl 2 -, CF 3 CHCl-, CF 3 CFCl-, CFCl 2 CF 2 -, CHFClCF 2 -, C 6 F 5 -, CHCl 2 CF 2 -, CH 3 CHFCH 2 -, CH 2 FCH(CH 3 )-, CF 3 CHFCF 2 -, CF 3 CF 2 CHFCF 2 -, HOCH 2 CF 2 CF 2 CH 2 -, CH 2 ClCF 2 -, and CF 3 CHClCF 2 -. -CZ 3 Z 4 CFZ 3 Z 4 wherein each of Z 3 and Z 4 independently represents a fluorine atom, a chlorine atom, a bromine atom, a CF 3 group or a hydrogen atom. wherein R f ' represents a fluorocarbon residue having from 1 to 16 carbon atoms. -CF 2 CX 1 X 2 H wherein each of X 1 and X 2 independently represents a fluorine atom, a chlorine atom or a hydrogen atom. -C n ,F 2n'-1 wherein n' is an integer of from 2 to 20. Examples of group (9) include the following groups of formulae (10) and (11): -C 3m F 6m-1 wherein m is an integer of 2 or more, preferably from 2 to 6. -C 2m' F 4m'-1 wherein m' is an integer of 2 or more, preferably from 2 to 10. -C n' F 2n' H wherein n' is an integer of from 2 to 20. Examples of group (12) include the following groups of formulae (13) and (14): -C 3m F 6m H wherein m is an integer of 2 or more, preferably from 2 to 6. -C 2m' F 4m' H wherein m' is an integer of 2 or more, preferably from 2 to 10. Specific examples of groups represented by formulae (9) to (14) include the following groups: CF 2 =CF-, CF 2 =CFCF 2 -, CF 3 CF=CF-, CF 3 CF 2 CF=CF-, (CF 3 ) 2 C=CF-, C 6 F 11 -, C 9 F 17 -, C 12 F 23 -, C 15 F 29 -, C 10 F 19 -, CF 3 CHFCF 2 -, C 6 F 12 H-, C 9 F 18 H-, C 4 F 8 H-, and C 10 F 20 H-. In addition, the following groups can also be used. CFCl=CF-, CFCl 2 CF 2 CF=CF-, CF 3 CCl=CF-, CCl 2 =CF-, CHCl=CF-, (CF 3 ) 2 CH-, CF 3 CFClCFCl- and -CF(C 2 F 5 )CH(CF 3 )CF 2 OC 6 H 4 -C 6 H 13 . Especially preferred examples of R f include an unsubstituted fluoroalkyl group having from 1 to 3 carbon atoms, -CF=CFCF 3 , -CF 2 CFClH, -CF=CFCl, and wherein n is an integer of from 0 to 6. With respect to the formula (C-1), when the total number of carbon atoms in R 1 and R 2 is 3 or less, the bioaccumulation of the compound (C-1) is disadvantageously high. On the other hand, when the total number of carbon atoms in R 1 and R 2 is 20 or more, the miscibility of the compound (C-1) with a hydrofluorocarbon refrigerant, such as HFC-134a, or a hydrofluoroether refrigerant is low, and also the availability of the material to be used for producing the compound (C-1) is very low. From the viewpoint of increasing stability, it is preferred that each of R 1 and R 2 in the formula (C-1) be an alkyl group, but not a hydrogen atom. With respect to R 1 and R 2 of the formula (C-1), each may independently have a substituent group and/or a linkage group. Examples of these substituent and linkage groups include unsaturated hydrocarbon groups; halogen atoms, such as a chlorine atom and a fluorine atom; and various polar groups containing oxygen, nitrogen, phosphorus or sulfur, such as a hydroxyl group, a thiol group, an alkoxy group, a nitrile group, a nitro group, an ether group, a thioether group, an ester group, a carbonyl group, a sulfonyl group, a sulfinyl group, a carboxyl group, a carboxylate group, an amino group, a thiocarbamate group, an amido group, an imido group, a pyridine group, a pyrimidine group, a piperidine group, a triazine group, a phosphine group, a benzoimidazole group, a phosphorous ester group, a triazole group, a tetrazole group, a thiazole group, and a thiadiazole group. Of them, a fluorine atom and an ether group are preferred from the viewpoint of improving stability. The number of such substituent group and/or linkage group in each of R 1 and R 2 is preferably 5 or less, more preferably 3 or less, still more preferably 1 or less. Specific examples of the compounds represented by formula (C-1) include the following compounds: The fluorine-containing aromatic compound of the present invention and represented by formula (C-1) can be synthesized by various methods. Hereinbelow, an illustrative mode of synthesis is described for various fluorine-containing aromatic compounds. The compounds of formula (C-1) may also be synthesized according to a similar procedure: (1) Reaction of a phenol or a thiophenol with a fluorine-containing olefin: A number of methods are known for the synthesis of fluorine-containing aromatic compounds by the reaction of phenols or thiophenols with fluorine-containing olefins. Representive examples of methods are illustrated below, wherein a perfluoroolefin is used as a fluorine-containing olefin: wherein Ar' represents a monovalent aromatic group, X represents an oxygen atom or a sulfur atom, and n' is an integer of from 2 to 20. Representative examples of reactions between phenols and fluorine-containing olefins, are indicated below. For example, Advance in Fluorine Chemistry, 4 , 50 (1965) indicates examples of reactions similar to those of formulae (15) and (16) in connection with the ionic reactions of the following various types of fluorine-containing olefins with phenols, alcohols or thiophenols. CF 2 =CF 2 , CF 2 =CFCl, CF 2 =CFBr, CF 2 =CFH, CF 2 =CHCl, CF 2 =CCl 2 , CHF=CCl 2 , CF 3 CF=CF 2 , CClF 2 CF=CF 2 , CF 3 CCl=CF 2 , CF 3 CF=CCl 2 , CF 3 CCl=CClF, CF 3 CH=CH 2 , CF 3 CH=CHCl, CF 3 CCl=CHCl, CF 3 CCl=CCl 2 , CF 3 CF 2 CF=CF 2 , CF 3 CF=CFCF 3 , (CF 3 ) 2 C=CF 2 , CF 2 =CF-CF=CF 2 , and CF 3 Cl=CClCF 3 wherein R 1 represents an alkyl group. CF 3 CCl=CClCF 3 , CCl 2 FCClFCF=CClF and CF 3 -(CF 2 ) 4 -CF=CF 2 Journal of American Chemical Society, 73 , 5831 (1951) discloses the reaction: wherein R 2 represents a hydrogen atom or an alkyl group, and X 1 and X 2 each independently represent a fluorine atom, a chlorine atom or a hydrogen atom. 142nd Meeting American Chemical Society, Atlantic City, N.J., Sept. 1962 Abs, P19U discloses the reaction: Journal of American Chemical Society, 82 , 5116 (1960) discloses the reaction: wherein X 3 represents a chlorine atom or a fluorine atom. Nippon Kagakukai-shi 1975, 311 discloses the reaction: wherein Y 1 represents a hydrogen atom, -OMe or -NO 2 , and X 4 represents a fluorine atom or -CF 3 . PhOH+CF 3 CF=CF 2 →CF 3 CHFCF 2 OPh Unsaturated bond-containing oligomers derived from various fluorine-containing olefins, such as a hexafluoropropene (HFP) oligomer of formula (24) below, a tetrafluoroethylene (TFE) oligomer of formula (25) below and a chlorotrifluoroethylene oligomer, can also be used as a raw material in the synthetic reactions as represented by formulae (15) and (16) above. C 3m F 6m wherein m is an integer of 2 or greater, preferably from 2 to 6. C 2m' F 4m' wherein m' is an integer of 2 or greater, preferably from 2 to 10. Examples of reactions of such oligomers include the following reactions: Bull. Chem. Soc. Japan, 49 502 (1976) discloses the reaction: wherein Et represents an ethyl group. Nippon Kagakukai-shi 1978 , 253 discloses the reaction: "Oligomer" edited by Okawara, Saegusa and Higashimura and published by Kodansha Scientific Ltd. (1976) pages 288 to 291, discloses representive examples of reactions between various TFE pentamers (C 10 F 20 ) or HFP trimers (C 9 F 18 ) and phenols, as represented by the following formulae: Journal of Fluorine Chemistry 54 , 162 (1991) discloses addition reactions between a perfluorovinyl ether and a phenol, as represented by formulae (34') and (34''): wherein R f represents -C 3 F 7 , -CF 2 CF(CF 3 )OC 3 F 7 or -CF 2 CF(CF 3 )OCF 2 CF 2 CO 2 CH 3 , and X represents a chlorine atom or a bromine atom. Izvest. Akad. Nauk S.S.S.R., Otdel. Khim. Nauk 1952 , 261-7 discloses addition reactions between a thiophenol and a chlorotrifluoroethylene or a tetrafluoroethylene, as represented by formula (34''') wherein X represents a chlorine atom or a fluorine atom. Bull. Soc. Chim. Fr., 1972, (8), 3202-5 discloses an addition reaction between a thiophenol and a chlorotrifluoroethylene as represented by formula (34''''). PhSNa + CF 2 = CClF → PhCF = CClF (2) Reactions between phenols or thiophenols and saturated fluorocarbons: A number of reaction schemes are possible in the reaction of phenols or thiophenols with saturated fluorocarbons for producing fluorine-containing aromatic compounds. Representive examples of such reaction schemes include the following reactions: Ar'X - + R f X 5 → Ar'XR f Ar'X 6 + R f 'X - → Ar'XR f ' wherein X represents an oxygen atom or a sulfur atom, X 5 and X 6 each independently represent a halogen atom, -OSO 2 Me, -OCOCF 3 , -OSO 2 CF 3 , -OSO 2 CCl 3 or -OSO 2 Cl, which are substituents readily liberated in the form of an anion, Ar' represents a monovalent aromatic group, and R f ' has the same meaning as defined for R f of formula (A), which represents a group capable of assuming an anion structure of the formula R f 'X - . Actual, Chem., 1987 ,151 discloses the reactions: wherein R 3 represents a hydrogen atom, 4-Cl, 4-Br, 2-MeO 2 C, 4-O 2 N, 2-O 2 N or 4-CF 3 , X 7 represents a fluorine atom, a chlorine atom or a bromine atom, and R 4 represents -SO 2 Me, -COCF 3 , -SO 2 CCl 3 , -SO 2 C 6 H 4 Me-P or -SO 2 Cl. "Chemistry of Organic Fluorine Compounds" Halsted Press, 2nd Edition, P279 discloses a number of methods for synthesizing a fluorine-containing ether compound and a fluorine-containing thioether compound, in which an alcohol, a phenol or a thiol is alkylated at oxygen atom or sulfur atom portions thereof. Journal of Organic Chemistry, 50 , 4047 (1985) wherein Z 1 represents a hydrogen atom, a methyl group, a methoxy group or a chlorine atom, and X represents an oxygen atom or a sulfur atom. Industrial and Engineering Chemistry, 39 , 412 (1947) discloses the reactions: Tetrahedron Letters, 22 , 323 (1981) discloses the reaction: wherein X represents an oxygen atom or a sulfur atom. Pure and Applied Chemistry, 59 , 1015 (1987) discloses a number of reactions of various fluorine-containing halide compounds represented by formula (42) below with phenoxides. CZ 2 Z 3 Z 4 CFZ 3 Z 4 wherein Z 2 represents a chlorine atom, a bromine atom or an iodine atom, and, Z 3 and Z 4 each represent a fluorine atom, a chlorine atom, a bromine atom, a CF 3 group or a hydrogen atom. Examples of such reactions include the following reactions: PhS - + CF 3 CCl 3 → PhSCCl 2 CF 3 PhO - + CF 2 ClCFCl 2 → PhOCF 2 CFCl 2 Journal of Organic Chemistry, 25 , 2009 (1960) discloses the reaction: wherein Z 5 and Z 6 each represent a hydrogen atom, a methyl group, a methoxy group, a nitro group, a methyl group or a chlorine atom. In addition, fluorine-containing aromatic compounds represented by formula (C-1) can be synthesized by appropriately applying methods for forming various types of ether linkages. For example, an ether formation reaction comprising reacting a hydroxyl group with an epoxy group as indicated below, can be utilized: wherein Ar' represents a monovalent aromatic group, and R f '' represents a fluorocarbon residue having from 1 to 16 carbon atoms. Further, a method in which fluorine atom or atoms are introduced into a precursor of the compound represented by formula (C-1) by various methods, may be available, or a method in which reaction products obtained by the various methods described above are converted into a desired compound represented by formula (C-1) using various reactions, may be available. For example, the following method can be mentioned, as disclosed in Actual. Chem., 1987, 151: wherein R 3 has the same meaning as defined for R 3 in formulae (36) and (37). The fluorine-containing olefin and the fluorine-containing compound, such as a saturated fluorocarbon, each of which is to be used in the above-mentioned reactions, can be synthesized by various known methods. For example, such methods include a synthetic method by halogen exchange disclosed in "Advances in Fluorine Chemistry" Butterworth, vol. 3, p181, a method disclosed in "Chemistry of Organic Fluorine Compounds" Halsted Press, and methods for producing fluoroolefin oligomers disclosed in Japanese Patent Application Laid-Open Specification No. 50-117705 and Japanese Patent Application Publication Specification Nos. 43-11885 and 47-22563. The methods set out above are not limiting, and various other methods can be employed. With respect to the alkyl- or alkyl derivative-substituted aromatic compound (B) which can be used in the present invention, there is no particular limitation as long as it is an oily material which satisfies the above-mentioned requirements. However, from the viewpoint of ease in handling, it is preferred that the compound (B) have a kinetic viscosity of from 0.1 to 500 cSt, preferably from 1 to 300 cSt, more preferably from 3 to 100 cSt as measured at 40 °C. The number of the at least one substituted aromatic nucleus in the compound (B) is preferably in the range from 1 to 4, more preferably 1 or 2, most preferably 1. When the number of the substituted aromatic nucleus in the compound (B) is 5 or more, the viscosity of the compound (B) tends to become too high. With respect to the proportion of the aromatic nucleus in the compound (B), it is preferred that the ratio of carbon atoms in the aromatic nucleus of the compound (B) to all carbon atoms in the compound (B) be in the range from 0.10 to 0.95. This ratio is more preferably in the range from 0.15 to 0.9, still more preferably from 0.20 to 0.8. When the ratio of carbon atoms in the aromatic nucleus of the compound (B) to carbon atoms in the compound (B) is less than 0.10, the miscibility of the compound (B) with the fluorine-containing aromatic compound (C-1) tends to be lowered, or the miscibility of the lubricant oil composition comprising the compound (C-1) and the compound (B) with a hydrofluorocarbon refrigerant or a hydrofluoroether refrigerant tends to be lowered. On the other hand, when the ratio of carbon atoms in the aromatic nucleus of the compound (B) to carbon atoms in the compound (B) is more than 0.95, the compound (B) tends to be likely to crystallize even around room temperature. It is preferred that the unsubstituted or substituted alkyl group as the substituent of the compound (B) have from 1 to 30, preferably from 4 to 25 carbon atoms. Examples of derivatives of the at least one substituted aromatic nucleus of the compound (B) include one in which at least two substituted aromatic nuclei selected from the group consisting of a substituted benzene nucleus and a substituted naphthalene nucleus are linked through a linkage group to form a multinuclear structure. The linkage group can be selected from the group consisting of a single bond and a bivalent group, such as an alkylene group, an ether group, an ester group, a carbonate group, a carbonyl group or a sulfonyl group. The derivative of the at least one aromatic nucleus of the compound (B) may be further substituted. A preferred form of the alkyl- or alkyl derivative-substituted aromatic compound (B) is described below. The preferred form of the alkyl- or alkyl derivative-substituted aromatic compound (B) is represented by the formula: wherein: each of Ar a and Ar b independently represents a benzene nucleus or a naphthalene nucleus, n 1 is an integer of from 0 to 4, preferably from 1 to 3, n 2 is an integer of from 0 to 3, preferably 1 or 2, n 3 is an integer of from 1 to 3, preferably 1 or 2, most preferably 1, n 4 is an integer of from 0 to 2, with the proviso that when n 4 is zero, n 1 is not zero and that when n 4 is not zero, (n 1 + n 2 ) is not zero, K is a linkage group selected from the group consisting of: 1) a single bond, 2) a bivalent group selected from the group consisting of an oxygen atom (-O-), a sulfonyl group and a carbonyl group, which is preferably -O-, and 3) an unsubstituted or substituted saturated hydrocarbon group having from 1 to 12 carbon atoms, preferably from 1 to 4 carbon atoms, most preferably 1 carbon atom and having a valence of from 2 to 4, preferably a valence of 2, and each of R 1 and R 2 independently represents an unsubstituted or fluorine-substituted alkyl group having from 1 to 30 carbon atoms, preferably from 4 to 25 carbon atoms, wherein a main chain of the unsubstituted or fluorine-substituted alkyl group optionally has at least one ether linkage introduced therein or to a terminal thereof, with the proviso that the ratio of the at least one ether linkage to all carbon atoms of the alkyl- or alkyl derivative-substituted aromatic compound of formula (B-1) is not more than 1/3, preferably not more than 1/5, wherein when n 1 is an integer of 2 to 4, the R 1 groups are the same or different; when n 2 is an integer of 2 or 3, the R 2 groups are the same or different; when n 3 is an integer of 2 or 3, the R 2 groups are the same or different and the Ar b groups are the same or different; and when n 4 is 2, the K groups are the same or different, the R 2 groups are the same or different and the Ar b groups are the same or different, wherein the alkyl- or alkyl derivative-substituted aromatic compound of formula (B-1) optionally has at least one hydrogen atom replaced with a polar group at a ratio of not more than 1/3, preferably not more than 1/5 relative to all hydrogen atoms of said alkyl- or alkyl derivative-substituted aromatic compound of formula (B-1), the polar group being selected from the group consisting of a chlorine atom, an unsubstituted or substituted amino group, an acyl group, an acyloxy group, a carboalkoxy group and a nitrile group. The alkyl- or alkyl derivative-substituted aromatic compound (B) optionally has at least one hydrogen atom replaced with a fluorine atom at a ratio of not more than 1/2 relative to all hydrogen atoms of the alkyl- or alkyl derivative-substituted aromatic compound (B). Examples of such fluorine-substituted compound (B) include 2,2,2-trifluoroethyl-substituted aromatic compounds, 3,3,3-trifluoropropyl-substituted aromatic compounds, and various fluorine-substituted alkyl benzenes, such as CF 3 CHFCF 2 -substituted alkyl benzenes. When the compound (B) has an alkoxy group substituted with a fluorine atom, it is preferred that the ratio of fluorine atom in the fluoroalkoxy group to carbon atom in the fluoroalkoxy group be less than 0.6. In the compound (B) represented by formula (B-1), at least two carbon atoms which are not a part of the aromatic nucleus may be linked through a single or double bond to form a ring structure. In the lubricant oil composition of the present invention, two or more types of the compound (B) may be employed in combination. The compound (B) may be employed in a mixed form with a non-aromatic hydrocarbon compound. When the compound (B) is employed in a mixed form with a non-aromatic hydrocarbon compound, the weight ratio of the compound (B) to the non-aromatic hydrocarbon compound is preferably 0.5 or more, more preferably 1.0 or more. Illustrative examples of the alkyl- or alkyl derivative-substituted aromatic compound (B) are described below. Representative examples of substituted aromatic compounds usable as the compound (B) include alkylbenzenes, alkylnaphthalenes, derivatives of alkylbenzenes, such as an alkylated biphenyl, a polyphenyl-substituted hydrocarbon and styrene oligomer, and derivatives of alkylnaphthalenes. From the viewpoint of economy, preferred is an alkylbenzene, which can be obtained at a low price. Examples of alkylbenzenes include a monoalkylbenzene, a dialkylbenzene, and a polyalkylbenzene having at least 3 alkyl groups as substituents. Of alkylbenzenes, a monoalkylbenzene and a dialkylbenzene, which are easily available, are preferred from the commercial viewpoint. As an alkylbenzene, any of a (branched) alkylbenzene and a (linear) alkylbenzene can be employed. A (branched) alkylbenzene is preferred to a (linear) alkylbenzene since the (branched) alkylbenzene exhibits a particularly good miscibility with a hydrofluorocarbon as a refrigerant. Of (branched) alkylbenzenes, those having at least one branched alkyl group having from 3 to 30 carbon atoms are preferred. More specific examples of the alkyl- or alkyl derivative-substituted aromatic compound (B) are described below. Such specific examples of the compound (B) include: a (branched) alkylbenzene represented by the formula: and (linear) alkylbenzenes respectively represented by the following formulae: and More specific examples of the compound (B) also include those respectively represented by the following formulae: and Examples of compounds represented by formula (49) above include those respectively represented by the following formulae: and More illustrative examples of the compound (B) also include those respectively represented by the following formulae: and In the above-mentioned formulae representing more illustrative examples of the compound (B): R represents a hydrogen atom or an alkyl group having 1 to 30, preferably 4 to 25 carbon atoms, R' represents a hydrogen atom, an alkyl group having 1 to 10, preferably 1 to 5 carbon atoms, an aralkyl group having 7 to 20, preferably 7 to 10 carbon atoms, an aryl group having 6 to 20, preferably 6 to 14 carbon atoms or a halogen-substitution product thereof, each of R 1 , R 2 and R 3 represents an alkyl group having 6 to 30, preferably 8 to 25 carbon atoms, R 4 represents an alkyl group having 4 to 20 carbon atoms, R 5 represents an alkyl group having 1 to 10 carbon atoms, R 6 represents a hydrogen atom or -CH 3 , n represents an integer of from 0 to 10, preferably 1 to 6, more preferably 1 to 3, m' represents an integer of from 1 to 19, n ' represents an integer of from 1 to 19, m' + n' is an integer of from 8 to 20, n 1 represents an integer of from 1 to 8, n 2 represents an integer of from 3 to 10, n 3 represents an integer of from 6 to 20, and n" represents an integer of from 2 to 4. Each of commercially available alkylbenzene products usable as the compound (B) is usually a mixture of a plurality of types of alkylbenzenes. In the above mentioned lubricant oil composition comprising the fluorine-containing aromatic compound (C-1) and the alkyl- or alkyl derivative-substituted aromatic compound (B), the fluorine-containing aromatic compound (C-1) is present in an amount of from 0.1 to 99.9 % by weight, preferably from 1 to 99 % by weight, more preferably from 5 to 95 % by weight, most preferably from 10 to 90 % by weight, based on the total weight of the fluorine-containing aromatic compound (C-1) and the alkyl- or alkyl derivative-substituted aromatic compound (B). When the ratio of the compound (C-1) is less than 0.1 % by weight as the lower limit, the miscibility of the lubricant oil composition with a hydrofluorocarbon refrigerant or a hydrofluoroether refrigerant cannot be satisfactorily improved, and the lubricating properties of the lubricant oil composition for these refrigerants cannot also be satisfactorily improved. On the other hand, when the ratio of the compound (C-1) is more than 99.9 % by weight as the upper limit, the low temperature flowability, the low moisture absorption properties, electrical insulation properties and the like cannot be satisfactorily improved. In the lubricant oil composition comprising the fluorine-containing aromatic compound (C-1) and the alkyl- or alkyl derivative-substituted aromatic compound (B), when the compound (C-1) is present in a relatively high amount, for example, from 40 to 99.9 % by weight, preferably 60 to 99.9 % by weight, even when it is employed in combination with a hydrofluorocarbon refrigerant or a hydrofluoroether refrigerant, a homogeneous refrigerant composition can be obtained over a wide temperature range. On the other hand, when the compound (B) is present in a relatively high amount in the lubricant oil composition comprising the compound (C-1) and the compound (B), and the lubricant oil composition is employed in combination with a hydrofluorocarbon refrigerant or a hydrofluoroether refrigerant, it is possible that a part of the refrigerant composition, which part is composed mainly of the compound (B), undergoes a phase separation depending on use conditions. However, since the compound (C-1) exhibits excellent affinity to any of the compound (B) and a refrigerant, such as a hydrofluorocarbon refrigerant and a hydrofluoroether refrigerant, even when a lubricant oil composition of the present invention having a relatively high ratio of the compound (B) is used, the compound (C-1) effectively serves as an agent for facilitating oil return to the compressor. Therefore, such a lubricant oil composition having a relatively high ratio of the component (B) can be advantageously used. For improving oil return to the compressor, the amount of the compound (C-1) in the lubricant oil composition comprising the compound (C-1) and the compound (B) is preferably 5 % by weight or more, more preferably 10 % by weight or more, still more preferably 40 % by weight or more, based on the total weight of the compound (C-1) and the compound (B). The larger the amount of the compound (C-1), the more the improvement in oil return to the compressor can be achieved. Therefore, a preferred upper limit of the amount of the compound (C-1) for improving oil return to the compressor is not particularly limited as long as the amount of the compound (C-1) is not larger than 99.9 % by weight, based on the total weight of the compound (C-1) and the compound (B). For improving the lubricating properties of the lubricant oil composition of the present invention, the amount of the compound (C-1) is from 0.1 to 99.9 %, preferably from 1 to 99 % by weight, more preferably from 10 to 90 % by weight, based on the total weight of the compound (C-1) and the compound (B). The compound (B) has a kinetic viscosity of from 0.1 to 500 cSt, preferably from 1 to 300 cSt, more preferably from 3 to 100 cSt as measured at 40 °C. With respect to the kinetic viscosity of the compound (C-1), there is no particular restriction. The lubricant oil composition comprising the compound (C-1) and the compound (B) has a kinetic viscosity as measured at 40 °C of from 2 to 500 cSt, preferably from 3 to 300 cSt, more preferably from 5 to 150 cSt. When the kinetic viscosity of the lubricant oil composition is too low, satisfactory lubricating properties in the compressor cannot be achieved. When the kinetic viscosity of the lubricant oil composition is too high, the revolution torque in the compressor becomes disadvantageously high. The compound (C-1) may be in a solid form as long as the kinetic viscosity of the lubricant oil composition comprising compound (C-1) and compound (B) is within the range from 2 to 500 cSt as measured at 40 °C. A conventional lubricant oil may optionally be added to the lubricant oil composition, and in such a case, there is no particular limitation on the kinetic viscosity of the conventional lubricant oil to be added, as long as the kinetic viscosity of the lubricant oil composition having the conventional lubricant oil added thereto is within the above-mentioned range from 2 to 500 cSt as measured at 40 °C. The above-mentioned lubricant oil composition can be advantageously used as a lubricant in a refrigerant system comprising a lubricant and at least one refrigerant selected from the group consisting of a hydrofluorocarbon and a hydrofluoroether, wherein the weight ratio of the lubricant oil composition to the at least one refrigerant is 99/1 to 1/99, preferably 95/5 to 5/95, more preferably 90/10 to 10/90. Examples of hydrofluorocarbon refrigerants usable with the lubricant oil composition to provide the above mentioned refrigerant composition include a hydrofluorocarbon having from 1 to 5 carbon atoms, preferably from 1 to 4 carbon atoms. Representative examples of such hydrofluorocarbons include fluoromethanes, such as HFC-32 (CH 2 F 2 ), fluoroethanes, such as HFC-134a (CF 3 CH 2 F), HFC-134 (CHF 2 CHF 2 ), HFC-143a (CF 3 CH 3 ), HFC-152a (CH 3 CHF 2 ), and HFC-125 (CF 3 CHF 2 ), fluoropropanes, such as CF 3 CH 2 CHF 2 , CF 3 CHFCF 3 , CHF 2 CF 2 CHF 2 , CF 3 CF 2 CF 3 , CF 3 CF 2 CH 3 , and CHF 2 CF 2 CH 2 F, fluorobutanes, such as CF 3 CF 2 CF 2 CH 3 and CF 3 CHFCHFCF 3 , fluoropentanes, such as CF 3 CHFCHFCF 2 CF 3 . These hydrofluorocarbons can be used individually or in combination. When the above-mentioned hydrofluorocarbon refrigerants are used in combination, preferred examples of mixed hydrofluorocarbon refrigerants include HFC-32/HFC-125, HFC-32/HFC-134a, HFC-32/HFC-125/HFC-134a, HFC-32/HFC-125/HFC-290(propane)/HFC-134a, HFC-125/HFC-134a, HFC-125/HFC-143a, HFC-125/HFC-143a/HFC-134a and HFC-32/HFC-125/HFC-143a. The above mixed refrigerants are promising as substitute refrigerants for replacing HCFC-22. Furthermore, a mixed refrigerant containing a chlorine-containing fluorocarbon, such as HCFC-22 (CHClF 2 ) or CFC-12 (CCl 2 F 2 ), in addition to a hydrofluorocarbon, can also be used in the refrigerant composition. In the mixed refrigerant comprised of a chlorine-containing fluorocarbon and a hydrofluorocarbon, the chlorine-containing fluorocarbon is used in an amount of from 0.01 to 80 % by weight, preferably from 0.01 to 60 % by weight, more preferably from 0.01 to 40 % by weight. When a conventional lubricant oil, such as polyalkyleneglycol or an ester oil, is contacted with a chlorine-containing refrigerant, even if the amount of the chlorine-containing refrigerant is small, the decomposition of the lubricant oil is accelerated, so that the lubricant oil cannot be practically used in the presence of a chlorine-containing refrigerant. By contrast, the lubricant oil composition is stable even in the presence of a chlorine-containing refrigerant. Therefore, for example, the lubricant oil composition is promising for use in retrofitting a conventional compressor employing a chlorine-containing refrigerant. (The term "retrofitting" used herein means to renew a compressor simply by replacing the refrigerant and the lubricant oil employed therein with fresh ones.) It has been found that the above-mentioned lubricant oil composition exhibits excellent miscibility not only with a hydrofluorocarbon refrigerant, but also with a hydrofluoroether refrigerant which is attracting attention because a hydrofluoroether has a global warming potential advantageously lower than that of a hydrofluorocarbon. As a hydrofluoroether refrigerant, various hydrofluoroethers can be used. However, from the viewpoint of lowering the global warming potential, it is preferred that the sum of the number of carbon atoms and the number of oxygen atoms of the hydrofluoroether be from 3 to 6. From this viewpoint, it is also preferred that the hydrofluoroether have at least one hydrogen atom in the molecule thereof. Examples of hydrofluoroether refrigerants usable in the refrigerant composition include the following compounds: CF 3 -O-CHF 2 , CF 3 -O-CH 2 F, CF 3 -O-CH 3 , CHF 2 -O-CHF 2 , and CHF 2 -O-CH 2 F; CF 3 -O-CF 2 -CHF 2 , CF 3 -O-CF 2 -CH 2 F, CF 3 -O-CF 2 -CH 3 , CF 3 -O-CHF-CF 3 , CF 3 -O-CHF-CHF 2 , CF 3 -O-CHF-CH 2 F, CF 3 -O-CHF-CH 3 , CF 3 -O-CH 2 -CF 3 , CF 3 -O-CH 2 -CHF 2 , CF 3 -O-CH 2 -CH 2 F, and CF 3 -O-CH 2 -CH 3 ; CHF 2 -O-CF 2 -CF 3 , CHF 2 -O-CF 2 -CHF 2 , CHF 2 -O-CF 2 -CH 2 F, CHF 2 -O-CF 2 -CH 3 , CHF 2 -O-CHF-CF 3 , CHF 2 -O-CHF-CHF 2 , CHF 2 -O-CHF-CH 2 F, CHF 2 -O-CHF-CH 3 , CHF 2 -O-CH 2 -CF 3 , CHF 2 -O-CH 2 -CHF 2 , and CHF 2 -O-CH 2 -CH 2 F; CH 2 F-O-CF 2 -CF 3 , CH 2 F-O-CF 2 -CHF 2 , CH 2 F-O-CF 2 -CH 2 F, CH 2 F-O-CF 2 -CH 3 , CH 2 F-O-CHF-CF 3 , CH 2 F-O-CHF-CHF 2 , CF 2 F-O-CHF-CH 2 F, CH 2 F-O-CH 2 -CF 3 , and CH 2 F-O-CH 2 -CHF 2 ; CH 3 -O-CF 2 -CF 3 , CH 3 -O-CF 2 -CHF 2 , CH 3 -O-CF 2 -CH 2 F, CH 3 -O-CHF-CF 3 , CH 3 -O-CHF-CHF 2 , and CH 3 -O-CH 2 -CF 3 ; CH 3 -O-CH 2 CF 2 CF 3 , CH 3 -O-CF 2 CHFCF 3 , CH 3 CH 2 -O-CF 2 -CHF 2 , CF 3 CH 2 -O-CH 2 -CF 3 , CF 3 CF 2 -O-CF 2 -CF 3 , CF 3 CF 2 CF 2 -O-CHFCF 3 , (CF 3 ) 2 CHCF 2 -O-CH 3 , and CF 3 CF 2 CH 2 -O-CF 2 CHF 2 ; and CF 3 -O-CF 2 CF 2 -O-CH 3 . With respect to the compound (C-1), for improving the miscibility with the compound (B), the ratio of fluorine atoms to the total number of fluorine and hydrogen atoms in the compound (C-1), is preferably in the range from 0.03 to 0.85, more preferably from 0.05 to 0.6, still more preferably from 0.1 to 0.5. With respect to fluorine-containing aromatic compound (C-1), a plurality of types can be used in the form of a mixture as the compound (C-1) to be mixed with the compound (B) to provide the above-mentioned lubricant oil composition. The compound (C-1) has a good miscibility with hydrocarbons. Examples of hydrocarbons include (1) mineral oils, such as paraffin mineral oil and naphthene mineral oil; (2) olefin (co)polymers; and (3) aromatic hydrocarbons, such as alkylbenzene, alkylnaphthalene, alkylated biphenyl, polyphenyl-substituted hydrocarbon, and stylene oligomer (the aromatic hydrocarbons including the alkyl- or alkyl derivative-substituted aromatic compound (B)). Therefore, the compound (C-1) can be advantageously used in a mixed form with above-mentioned hydrocarbon oils. Since the compound (C-1) exhibits an good miscibility with the alkyl- or alkyl derivative-substituted aromatic compound (B), such as alkylbenzene, even when the compound (C-1) is mixed with a large amount of the compound (B) to provide the lubricant oil composition, the good miscibility of the compound (C-1) with a hydrofluorocarbon refrigerant is not sacrificed, and the resultant lubricant oil composition is effectively improved in physical properties, such as low temperature fluidity, low moisture absorption properties, and electrical insulation properties. Further, the compound (C-1) exhibits good miscibility with any of a hydrocarbon and a hydrofluorocarbon, so that they can be used as an effective additive for facilitating oil return to the compressor in a refrigeration system employing a lubricant oil composed of a hydrocarbon, such as mineral oil, or an aromatic hydrocarbon or derivatives thereof, such as alkylbenzene. A lubricant oil composition obtained by mixing the compound (C-1) with the compound (B) is a very excellent lubricant oil as evaluated from the practical viewpoint, since it is extremely improved in all of the properties required for a lubricant oil, such as miscibility with HFC refrigerants, low temperature fluidity, low moisture absorption properties, electrical insulating properties and lubricating properties. The fluorine-containing aromatic compound (C-1) has an extremely excellent stability. As disclosed in Japanese Patent Application Laid-Open Specification No. 5-86382, a conventional lubricant oil composed of nonylphenol or dodecylphenol which are represented by the below-indicated formulae, undergoes oxidation and heat decomposition when heated in the air. By contrast, the compound (C-1) is not decomposed even when heated at 175 °C in the air for a long period of time. When the compound (C-1) is subjected to testing for stability in which the compound (C-1) is heated, individually or in mixture thereof, in the presence of a metal, such as copper, brass, aluminum or carbon steel and in the presence of an HFC refrigerant, such as HFC-134a, excellent results are obtained such that all of the compound (C-1) and the HFC refrigerant are stable even at 175 °C and that the surface of the metal does not show any appreciable change. Further, when a lubricant oil composition prepared by mixing the compound (C-1) with the compound (B) is subjected to the same stability testing as mentioned above, excellent results are also obtained such that all of the compound (C-1), the compound (B) and the HFC refrigerant are stable, and that the surface of the metal does not show any appreciable change. The compound (C-1) exhibits low moisture absorption properties. Further, it should be noted that when the compound (C-1) is mixed with the compound (B), a moisture absorption of the resultant lubricant oil composition is further remarkably lowered, so that the composition is free from problems, which have hitherto been caused by the presence of water in the refrigeration system, such as water freezing, metal corrosion and accelerated hydrolysis of an HFC refrigerant, such as HFC-134a. Furthermore, it should be noted that when the compound (C-1) is mixed with the compound (B), a lowering of volume resistivity, which has been frequently caused due to moisture absorption, can be markedly prevented. When a chemical substance is released in the natural environment (hydrosphere, pedosphere and atmosphere), the more stable the substance, the greater the probability that the substance will be in contact with living organisms. Accordingly, a relatively stable substance is likely to be taken and accumulated in living organisms, thereby polluting the organisms. From the standpoint of environmental toxicology, the present inventors have made studies. As a result, it has been found that the degree of bioaccumulation, i.e., bioconcentration, is low with respect to the compound (C-1). Further, the lubricating properties of each of the fluorine-containing compound (C-1) has been evaluated in the presence or absence of a hydrofluorocarbon. As a result, it has been found that, irrespective of the presence or absence of a hydrofluorocarbon, the compound (C-1) exhibits markedly excellent extreme pressure property (load at failure), abrasion resistance and coefficient of abrasion. For example, most of the fluorine-containing aromatic compounds of formula (C-1) exhibit much more excellent lubricating properties than conventional lubricant oils for use in refrigeration equipment, such as a mineral oil and alkylbenzene, and candidate lubricant oils for refrigeration equipment oil for HFC-134a, such as polyalkylene glycols and polyol ester oils. Further, it has unexpectedly been found that as shown in Example 62, the lubricant oil composition comprised of the fluorine-containing aromatic compound (C-1) and the alkyl- or alkyl derivative-substituted aromatic compound (B) has excellent anti-wear properties, as compared to the alkyl- or alkyl derivative-substituted aromatic compound (B) alone as well as the fluorine-containing aromatic compound (C-1) alone. The above-mentioned lubricating properties can be measured by means of various testers. For example, extreme pressure resistance and anti-wear properties can be measured by Falex tester. For further improving the anti-wear properties and extreme pressure resistance properties of the lubricant oil composition comprising a fluorine-containing aromatic compound (C-1) and an alkyl- or alkyl derivative-substituted aromatic compound (B), load carrying additives, such as oiliness agents, anti-wear agents and extreme pressure agents, can be added to the lubricant oil composition. From the above viewpoint, fluorine-containing compound (C-1) is advantageous in that it exhibits excellent miscibility with various types of conventional additives. With respect to the usefulness of the above-mentioned additives, reference can be made to, for example, "Additives for Petroleum Products" (published by Saiwai Syobou, Japan, 1979), in which oiliness agents are defined as additives capable of lowering a coefficient of abrasion by adsorption thereof onto a metal surface; anti-wear agents are defined as additives capable of effectively preventing wear under relatively low load; and extreme pressure agents are defined as additives capable of preventing seizing and wear by a reaction thereof with a metal surface under high temperature and high pressure conditions. In the above reference, it is also described that some additives not only serve as a monofunctional agent functioning only as oiliness agent, anti-wear agent, or extreme pressure agent, but also as a multifunctional agent for common purpose of the above-mentioned agents. For example, there can be mentioned an additive which can function not only as an oiliness agent, but also as an anti-wear agent and an extreme pressure agent. Examples of oiliness agents include carboxylic acids, alcohols, phenols, esters, amides and carboxylic salts. Examples of carboxylic acids include higher fatty acids, hydroxyaryl fatty acids, caboxylic acid-containing polyhydric alcohol esters and aromatic carboxylic acids. Specific examples of the above-mentioned carboxylic acids include linear saturated fatty acids, such as caproic acid, caprylic acid, capric acid, undecylic acid, lauric acid, myristic acid, palmitic acid, pelargonic acid, stearic acid, arachic acid, cerotic acid and lacceric acid; branched saturated fatty acids, such as isotridecanoic acid, isomyristic acid, isostearic acid and isoarachic acid; and unsaturated fatty acids, such as oleic acid and linoleic acid. Examples of alcohols include higher alcohols and unesterified hydroxyl group-containing polyhydric alcohol esters. Specific examples of the above-mentioned such higher alcohols and such polyhydric esters include lauryl alcohol, cetyl alcohol, stearyl alcohol, oleyl alcohol, glycerol monooleic ester, glycerol monostearate and glycerol dilaurate. Examples of phenols include alkylphenols and polyhydric phenols. Specific examples of the above-mentioned phenols include 3-pentadecylphenol, 4-heptyiphenol, octylphenol, nonylphenol, dodecylphenol and an alkylcatechol. Examples of esters include higher fatty esters (such as methyl laurate and methyl oleate), polyhydric alcohol esters, and acrylates. Examples of amides include higher fatty amides (such as lauric amide and oleic amide). Examples of carboxylates include salts of alkaline metals (e.g., sodium, potassium and the like), salts of alkaline earth metals, (e.g., magnesium, calcium and the like), and carboxylates of other metals, such as aluminum. Examples of other types of the load carrying additives include sulfur compounds, nitrogen compounds, halogenated compounds, phosphorus compounds, silicone compounds, and metal-containing compounds. Examples of sulfur compounds include thiophene and derivatives thereof, such as benzothiophene; monosulfides, such as di-n-dodecyl sulfide and dibenzil sulfide; disulfides, such as diphenyl disulfide; polysulfides; sulfones; thiosulfinates; sulfurized oils and fats; thiocarbonates; thiazoles; methanesulfonates; thioacetic acids, such as n-dodecylthioacetic acid; and alkylmercaptans, such as n-octadecylmercaptan. Examples of nitrogen compounds include benzotriazole derivatives, such as an alkyl-substituted benzotriazole. Examples of halogenated compounds include paraffin chrolide; chlorinated hydrocarbons, such as a chlorofluorocarbon (e.g., chlorotrifluoroethylene oligomer); chlorinated compounds, such as chlorinated carboxylic acid derivatives; polar group-containing fluorine compounds, such as fluorinated aliphatic alcohols, fluorinated aliphatic carboxylic acids, fluorinated aliphatic carboxylic esters, perfluoropolyethercaboxylic acids, perfluoropolyethercarboxylic esters, perfluoroalkyltriazines and perfluoropolyethertriazine; fluorinated compounds other than the above-mentioned polar group-containing fluorine compounds, such as graphite fluoride and ethylene fluoride oligomers; brominated compounds, such as alkane bromides, alkene bromides and alkyne bromides; and iodinated compounds, such as iodinated hydrocarbons. Examples of phosphorus compounds include phosphoric esters, such as phosphoric monoesters, phosphoric diesters, phosphoric triesters and halogenophosphoric esters; phosphonic esters, such as phosphonic monoesters, phosphonic diesters, phosphonic triesters and halogenophosphonic esters; tertiary phosphines; tertiary phosphine oxides; tertiary phosphine sulfides; phosphonic esters; phosphonous acid esters; phosphinic esters; phosphinous acid esters; thiophosphoric esters, such as thiophosphoric triesters; thiophosphonic esters; thiophosponous acid esters; thiophosphinic esters; phosphoroamidates; amine salts of acid phosphoric esters; and phosphazenes. Examples of silicone compounds include organosilicon compounds, such as silicone fluorides and carboxyl group-containing silicones. Examples of metal-containing compounds include salts of naphthenic acid, such as zinc naphthenates and lead naphthenates; salts of fatty acids, such as fatty acid leads; thiophosphates, such as zinc dithiophosphates and antimony dithiophosphates; salts of thiocarbamic acid, such as zinc dithiocarbamate, antimony dithiocarbamate and lead dithiocarbamates; organomolybdenum compounds, such as molybdenum oxysulfide dithiocarbamate and oxymolybdenum sulfide phosphorothioate; organotin compounds; organogermanium compounds; organo-titanium compounds; boric esters; organosilicates, such as diethylsilicate; and metal sulfides, such as iron sulfide; metal chlorides, such as iron chloride; and composites comprised of some of the above metal compounds. Specific examples of the above-mentioned polar group-containing fluorine compounds include fluorinated aliphatic alcohols, such as 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctanol, 1H,1H,7H-dodecafluoro-1-heptanol, 1H,1H,11H-eicosafluoro-1-undecanol and 2,2,3,3,4,4-hexafluoro-1,5-pentanediol; fluorinated aliphatic carboxylic esters, such as perfluoromethyl octanate and perfluoromethyl nonanoate; perfluoropolyethercarboxylic esters, such as hexafluoropropene oxide oligomer dicarboxylate and perfluoro-2,5-dimethyl-3,6-dioxanonanoate; fluorinated aliphatic carboxylic acids, such as perfluorononanoic acid; and perfluoropolyethercarboxylic acids, such as perfluoro-2,5-dimethyl-3,6-dioxanonanoic acid. Specific examples of the above-mentioned phosphorus compounds include orthophosphoric acid esters, such as tricresylphosphate, triphenylphosphate, triisopropylphenylphosphate, tris(2-ethylhexyl)phosphate, di(2-ethylhexyl)tridecylphosphate, di(2-ethylhexyl) allylphosphate, trioctylphosphate, trilaurylphosphate, tristearylphosphate, trioleylphosphate, tris[poly(oxyethylene)tridecyl]phosphate, tris[poly(oxyethylene)-2-ethylhexyl]phosphate, tris[poly(oxyethylene)isooctyl]phosphate, tris[poly(oxyethylene)poly(oxypropylene)-n-octyl]phosphate, tris[poly(oxyethylene)carbonyl-1-ethylpentyl]phosphate, tris[poly(oxyethylene)poly(oxypropylene)carbonyl-1-ethylpentyl]phosphate, tris[poly(oxyethylene)propyleneoxycarbonyl-1-methylvinyl]phosphate, tris[3-poly(oxyethylene)-methyl-2-methylpropionate]phosphate, tris[poly(oxyethylene)-2-hydroxyoctyl]phosphate, tris(p-octylphenoxyethylene)phosphate, tris[poly(oxyethylene)-poly(oxypropylene)-p-methylphenoxy]phosphate, tris[4-poly(oxyethylene)ethylphenylacetate]phosphate, tris[poly(oxyethylene)poly(oxypropylene)-p-butoxyphenyl]phosphate, 2-ethylhexyl[poly(oxyethylene)-2-ethylhexyl]phosphate and polyoxyalkylene. bis(diaryl)phosphate; acid phosphoric esters, such as ditetradecyl acid phosphate, dipentadecyl acid phosphate, dihexadecyl acid phosphate, diheptadecyl acid phosphate, dioctadecyl acid phosphate, di(polyoxyethlenenonylphenylether)phosphate; amine salts of acid phosphoric esters, such as salts of the above-mentioned acid phosphoric esters, formed with amines, including methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, heptylamine, octylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, diheptylamine, dioctylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, tripentylamine, trihexylamine, triheptylamine and trioctylamine; chlorinated phosphoric esters, such as tris(dichloropropyl)phosphate, tris(chloroethyl)phosphate, polyoxyalkylene·bis[di(chloroalkyl)]phosphate and tris(chlorophenyl)phosphate; brominated phosphoric esters, such as tris(tribromophenyl)phosphate, tris(dibromophenyl)phosphate and tris(2,4-di-tert-butylphenyl)phosphate; fluorinated phosphoric esters, such as tris(polyfluoroalkyl)phosphate and tris(polyfluorophenyl)phosphate; phosphites, such as dibutylphosphite, tributylphosphite, dipentylphosphite, tripentylphosphite, dihexylphosphite, trihexylphosphite, diheptylphosphite, triheptylphosphite, dioctylphosphite, trioctylphosphite, dinonylphosphite, didecylphosphite, diundecylphosphite, triundecylphosphite, didodecylphosphite, tridodecylphosphite, diphenylphosphite, triphenylphosphite, dicresilphosphite, tricresilphosphite, triisodecylphosphite, diphenyloctylphosphite, diphenyldecylphosphite, dilaurylhydrogenphosphite, dioleylhydrogenphosphite, tris(2,4-di-tert-butylphenyl)phosphite, trinonylphenylphosphite, polyoxyalkylene·bis(diaryl)phosphite, 1,1,3-tris(2-methyl-4-ditridecylphosphite-5-tert-butylphenyl)butane, tetraphenyldipropyleneglycoldiphosphite and tetradecyldiethyleneglycoldiphosphite; phosphonic esters, such as 0,0-dimethyldodecylphosphonate, 0,0-diethyldodecylphosphonate, O,O-di-n-butyldecylphosphonate, O,O-di-2-ethylhexyldodecylphosphonate, O,O-di-2-ethylhexyl-2-ethylhexylphosphonate, O,O-di-2-ethylhexylisooctylphosphonate, O,O-di-2-ethylhexylphenylphosphonate, O,O-dimethylphosphonomethylene(dimethyl)succinate, O,O-di-2-ethylhexyl-3-phosphnomethylpropionate, O,O-di-2-ethylhexyltris(ethyleneglycol)methylenephosphonate, O,O-di(decylpolyoxyethylene)phosphonate, O,O-di-2-ethylhexylhydroxymethylenephosphonate and O,O-di-2-ethylhexylphosphonomethylenepolyethyleneglycol; and phosphinic esters, such as O-alkyldialkylphosphinate. Each of the above-mentioned load carrying additives can be used individually or in combination thereof, or in combination with other additives. When the additive is incorporated in the lubricant oil composition which comprises a fluorine-containing aromatic compound (C-1) and an alkyl- or alkyl derivative-substituted aromatic compound (B), the amount of the additive is preferably in the range of from 0.01 to 25 % by weight, more preferably from 0.05 to 5.0 % by weight, still more preferably from 0.1 to 2.0 % by weight, based on the weight of the lubricant oil composition. When the amount of the additive contained in the lubricant oil composition is smaller than 0.01 % by weight, anti-wear properties and extreme pressure properties thereof cannot be satisfactorily improved. On the other hand, when the amount of the additive is greater than 25 % by weight, the properties of the lubricant oil composition for use thereof as a lubricant in refrigeration equipment (such as electrical insulation properties) are adversely affected and, therefore, the composition cannot be practically used. When the lubricant oil composition is used as a refrigerant oil, an anti-corrosive can also be added thereto for improving abrasion resistance of a metal surface of a refrigeration system. Examples of anti-corrosives include carboxylic acids, carboxylates, sulfonates, esters, amines, phosphoric esters, epoxy compounds and nitrogen-containing heterocyclic compounds. Examples of carboxylic acids include oleic acid and stearic acid. Examples of carboxylates include salts of fatty acids, such as lanolin fatty acids, which salts are formed with metals, such as Mg, Ca and Ba. Examples of sulfonates include salts of petroleum sulfonic acids, dinonylnaphthalenesulfonic acids, and alkylbenzenesulfonic acids, which salts are formed with metals, such as Na, Mg, Ca and Ba. Examples of esters include sorbitan monofatty acid esters (such as sorbitanmonoolate and sorbitanmonolaurate) and pentaerythritol monofatty acid esters. Examples of amines include aromatic amines (such as N-phenyl-α-naphthylamine), aliphatic amines and rosin amines. Examples of phosphoric esters include phosphoric monoesters and salts thereof, phosphoric diesters and salts thereof, phosphoric triesters (such as triphenylphosphate) and phosphites (such as triphenylphosphite). Examples of epoxy compounds include glycidyl ethers (e.g., arylglycidyl ethers, such as phenylglycidyl ether; and alkylgly cidyl ethers, such as 2-ethylhexylglycidyl ether); glycidyl esters (e.g., aromatic carboxylic acid glycidyl esters, such as phthalic acid diglycidyl ester), saturated aliphatic carboxylic acid glycidyl esters (such as 2-ethyl hexanoic acid glycidyl ester and decanoic acid glycidyl ester), unsaturated aliphatic carboxylic acid glycidyl esters, epoxidated fatty acid monoester (e.g., epoxystearic acid ester with butyl, hexyl, benzyl, cyclohexyl, methoxyethyl, octyl, phenyl or butylphenyl). Examples of nitrogen-containing heterocyclic compounds, such as benzotriazole and derivatives thereof (such as alkyl group-substituted benzotriazoles, e.g., 5-methyl-lH-benzotriazole); imidazole and derivatives thereof; benzoimidazole and derivatives thereof, e.g., 2-(alkyldithio)benzoimidazole; and 1,3,4-thiadiazole polysulfide. As an example of the other compound than the above-mentioned compounds, which can be used as anti-corrosives, there can be mentioned zinc dialkyldithiophosphate. Each of the above-mentioned anti-corrosives can be used individually or in combination thereof, or in combination with other types of additives. When the anti-corrosive is incorporated in the lubricant oil composition which comprises a fluorine-containing aromatic compound (C-1) and an alkyl- or alkyl derivative-substituted aromatic compound (B), the amount of the anti-corrosive is preferably in the range of from 0.0001 to 25 % by weight, more preferably from 0.001 to 5.0 % by weight, still more preferably from 0.1 to 2.0 % by weight, based on the weight of the lubricant oil composition. When the amount of the anti-corrosive contained in the lubricant oil composition is smaller than 0.0001 % by weight, anti-corrosive properties cannot be satisfactorily improved. On the other hand, when the amount of the anti-corrosive is greater than 25 % by weight, the properties of the lubricant oil composition for use thereof as a lubricant in refrigeration equipment (such as electrical insulation properties) are adversely affected and, therefore, the composition cannot be practically used. The above-mentioned lubricant oil composition can also be used in combination with still other types of additives, such as antioxidants, antifoaming agents, detergent-dispersants, viscosity index improvers, pour point improvers, metal deactivating agents and the like. Examples of antioxidants include phenols (e.g., 2,6-di-tert-butyl-p-cresol) and aromatic amines (e.g., α-naphtylamine). Examples of antiforming agents include silicon oils (e.g., dimethylsiloxane) and organosilicates. Examples of detergent-dispersants include sulfonates, phenates and succinimide. Examples of viscosity index improvers formed of various types of polymers, such as polymethacrylates. Examples of pour point improvers include diesters, polyalkylene glycols and triglyceride. Examples of metal deactivating agents include N,N'-disalicylidene-1,2-diaminoethane and acetylacetone. When at least one additive selected from the group consisting of the above-mentioned additives is added, the lubricant oil composition can be more advantageously used for various refrigeration systems, such as refrigerators, freezers, car air conditioners and room air conditioners, in which, from the viewpoint of the environmental protection, substitute refrigerants (e.g., HFC-134a) are used for conventional chlorine-containing refrigerants, such as CFC-12 and HCFC-22. The compound (C-1) can be advantageously used as a lubricant oil in the refrigeration system employing HFC refrigerants or HFE refrigerants. Further, the compound (C-1) can also be used in combination with other compounds (A). The compound (C-1) has a hybrid structure formed of at least one fluorocarbon group and at least one hydrocarbon group and, hence, it exhibits excellent miscibility with a variety of oils, e.g., hydrocarbons [which hydrocarbons include the compound (B)]. Accordingly, the compound (C-1) can be advantageously used as an additive in a refrigerant system using in combination an HFC refrigerant and a hydrocarbon lubricant, such as an ester oils, a polyalkylene glycol oil, an alkylbenzene or mineral oil (which is well-known to be unsatisfactory in miscibility with the HFC refrigerant), so that the oil return properties can be remarkably improved. The lubricant oils, which can be used with the compound (C-1) are, for example, hydrocarbons, such as naphthene mineral oil, paraffin mineral oil, alkylbenzene, alkylnaphthalene and poly-α-olefin; ether compounds, such as polyalkylene glycol and polyphenyl ether; fluorine-containing compounds, such as perfluoropolyether, perfluoropolyether substituted with polar substituents (e.g., a carbonyl-containing group, such as a carboxyl group, a carboxylate group, an amide group, a ketone group and an ester group; a hydroxyl group, an amino group, an imide group, an ether group, a benzoimidazol group, a phosphite group, a phosphine group, a nitril group, a phosphotriazine group and a triazine group), polychlorotrifluoroethylene and chlorofluorocarbon; ester compounds, such as polyol ester, and mixed ester; carbonates, such as polycarbonate; silicon-containing compounds, such as silicate, silicone, and fluorosilicone; phosphorus-containing oils, such as aryl phosphate, alkylaryl phosphate, and alkyl phosphate. From the above-mentioned conventional oils, one or more appropriate oils can be selected and added, taking into consideration the viscosity and the lubricating properties of the resultant lubricant oil composition containing such oils. When the compound (C-1) is added to a polar oil, such as ester oil, polyalkylene glycol oil and carbonate oil, the polar oil can be improved with respect or properties, such as low moisture absorption properties, stability, and lubricating properties. For further improving the abrasion resistance properties and extreme pressure resistance properties of the lubricant oil comprising a fluorine-containing aromatic compound (C-1), it is preferred that the same type of additives as mentioned above for the lubricant oil composition be also added. The same amounts of the additives (% by weight, based on the total amount of the lubricant oil) as mentioned above for the lubricant oil composition can be employed for the lubricant oil (C-1). It has been found that the compound (C-1) exhibits excellent miscibility not only with a hydrofluorocarbon refrigerant, but also with a hydrofluoroether refrigerant which is attracting attention because a hydrofluoroether has a global warming potential advantageously lower than that of a hydrofluorocarbon. Further, the fluorine-containing aromatic compound (C-1) exhibits various advantageous properties, such as excellent miscibility with various types of oils, low bioaccumulation, high stability and excellent lubricating properties. Therefore, the compound (C-1), even if not mixed with compound (B), can be used, individually or in mixture thereof or in a mixed form with other oils, as a lubricant oil which is excellent not only as a lubricant oil for a refrigerant system, but also, for example, as a lubricant oil for a magnetic recording medium, a compressor oil, an operating oil, a rolling oil, a gear oil, a traction drive oil, an engine oil and a base oil for grease. Furthermore, the compound (C-1) can also be used, for example, as an agent for improving the durability or lubricating properties of various types of oils, an agent for improving the surface characteristics of a polymer, a mold release agent, an agent for improving miscibility, and a base oil for an electroviscous fluid or a magnetic fluid. However, uses of the compound (C-1) of the present invention are not limited to the above-mentioned examples. When at least one additive selected from the group consisting of the above-mentioned additives is added, the lubricant oil (C-1) of the present invention can be more advantageously used for various refrigeration systems, such as refrigerators, freezers, car air conditioners and room air conditioners, in which, from the viewpoint of the environmental protection, substitute refrigerants (e.g., HFC-134a) are used for conventional chlorine-containing refrigerants, such as CFC-12 and HCFC-22. BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described in greater detail with reference to the following Referential Examples, Examples and Comparative Examples, which should not be construed as limiting the scope of the present invention. The kinetic viscosity of a lubricant oil can be determined by measuring the viscosity by means of 'various viscometers. As the viscometer to be used for determining the kinetic viscosity, there can be mentioned a capillary viscometer, such as a Ubbellohde viscometer, an Ostward viscometer or a Cannon-Fenske viscometer, a rotational viscometer, and a falling ball viscometer. In the present invention, an E-type rotational viscometer (manufactured and sold by Tokyo Keiki, Japan) is used. In the Referential Examples, Examples and Comparative Examples, a compound, which satisfies the abovementioned formula (A) but does not satisfy the above-mentioned formula (C-1), is simply referred to as a "compound (A)". Referential Example 1 (Comparative) In accordance with the method described in Example 54 of Unexamined Japanese Patent Application Laid-Open Specification No. 5-86382, comparative oil [S1] is synthesized as follows. 68.7 g of 2,2-bis(4-hydroxyphenyl)propane (hereinafter referred to simply as "bisphenol A"), 6.2 g of potassium hydroxide, 120 ml of dimethylsulfoxide and 1 ml of water are charged into a microcylinder having a capacity of 500 ml as a reactor, thereby obtaining a mixture. The reactor is heated to 60 °C by means of an oil bath, and the mixture is stirred at 60 °C under 'atmospheric pressure for 5 hours, to thereby obtain a solution. The inside of the reactor is degassed and then, inert gas N 2 is charged to restore atmospheric pressure. The reactor is heated to 60 °C by means of the oil bath, followed by introduction of tetrafluoroethylene, thereby starting a reaction. While feeding tetrafluoroethylene so as to maintain the pressure in the reactor (gauge pressure) at 3 to 4 kg/cm 2 , the reaction is carried out for about 5 hours to thereby obtain a reaction mixture. After the reaction, the dimethylsulfoxide is distilled off from the reaction mixture at 150 °C under about 5 mmHG to obtain a reaction product. The obtained reaction product is washed with about 100 ml of purified water 5 times. Thus, 130 g of a colorless, transparent oil (containing 99 % by weight of the comparative oil [S1]) is obtained. Simple distillation (the boiling point is about 150 °C under about 0.1 to 0.3 mmHg) and subsequently, separation treatment using a silica gel column are conducted to thereby isolate the comparative oil [S1]. The thus isolated oil [S1] is analyzed by infrared absorption spectrometry and mass spectrometry [m/e 428 (M + ), 413 (M + -CH 3 )] to thereby confirm that the oil [S1] is a compound having the following structural formula: The kinetic viscosity of the oil [S1] at 40 °C is 26 cSt. Referential Example 2 (comparative) Substantially the same procedure as in Referential Example 1 is repeated except that chlorotrifluoroethylene is used in place of tetrafluoroethylene, and that the amount of water to be added is changed from 1 ml to 44 ml, to thereby obtain a colorless, transparent oil [S2] comparative oil (yield: 99 %). The thus obtained comparative oil [S2] is analyzed by gas chromatography. As a result, it is found that the obtained oil [S2] has a purity of 99.9 % with respect to a desired product. The obtained oil [S2] is also analyzed by infrared absorption spectrometry and mass spectrometry [m/e 460, 462 (M + ), 445, 447 (M + -CH 3 )] to thereby confirm that the oil [S2] is a compound having the following structural formula: The kinetic viscosity of the oil [S2] at 40 °C is 57 cSt. Referential Example 3 (present invention) Oil [S3] is obtained in substantially the same manner as in Referential Example 1 except that compound [G1] shown below is used in place of bisphenol A (yield: 95 %). From the results of infrared absorption spectrometry shown in Fig. 1 and mass spectrometry [m/e 470 (M + )], it is confirmed that the oil [S3] is a compound having the following structural formula: The kinetic viscosity of the oil [S3] at 40 °C is 109 cSt. Referential Example 4 (present invention) Oil [S4] is obtained in substantially the same manner as in Referential Example 1 except that compound [G2] shown below is used in place of bisphenol A (yield: 90 %). From the results of infrared absorption spectrometry and mass spectrometry [m/e 498 (M + )], it is confirmed that the oil [S4] is a compound having the following structural formula: The kinetic viscosity of the oil [S4] at 40 °C is 112 cSt. Referential Example 5 (present invention) Oil [S5] is obtained in substantially the same manner as in Referential Example 1 except that compound [G3] shown below is used in place of bisphenol A (yield: 88 %). From the results of infrared absorption spectrometry and mass spectrometry [m/e 498 (M + )], it is confirmed that the oil [S5] is a compound having the following structural formula: The kinetic viscosity of the oil [S5] at 40 °C is 250 cSt. Referential Example 6 (present invention) Oil [S6] is obtained in substantially the same manner as in Referential Example 1 except that compound [G1] shown in Referential Example 3 is used in place of bisphenol A, that chlorotrifluoroethylene is used in place of tetrafluoroethylene, and that the amount of water to be added is changed from 1 ml to 44 ml (yield: ·95 %). From the results of infrared absorption spectrometry and mass spectrometry [m/e 502, 504 (M + )], it is confirmed that the oil [S6] is a compound having the following structural formula: The kinetic viscosity of the oil [S6] at 40 °C is 230 cSt. Referential Example 7 (comparative) Comparative Oil [S7] is obtained in substantially the same manner as in Referential Example 1 except that compound [G4] shown below is used in place of bisphenol A (yield: 94 %). From the results of infrared absorption spectrometry and mass spectrometry [m/e 442 (M + )], it is confirmed that the oil [S7] is a compound having the following structural formula: The kinetic viscosity of the oil [S7] at 40 °C is 50 cSt. Referential Example 8 (comparative) Comparative Oil [S8] is obtained in substantially the same manner as in Referential Example 1 except that compound [G5] shown below is used in place of bisphenol A (yield: 91 %). From the results of infrared absorption spectrometry and mass spectrometry [m/e 456 (M + )], it is confirmed that the oil [S8] is a compound having the following structural formula: The kinetic viscosity of the oil [S8] at 40 °C is 115 cSt. Referential Example 9 (comparative) Comparative Compound [S9] is obtained in substantially the same manner as in Referential Example 1 except that compound [G6] shown below is used in place of bisphenol A (yield: 96 %). The compound [S9] is solid at room temperature. From the results of infrared absorption spectrometry and mass spectrometry [m/e 456 (M + )], it is confirmed that the compound [S9] is a compound having the following structural formula: Referential Example 10 (comparative) Comparative oil [S10] is obtained in substantially the same manner as in Referential Example 1 except that p-n-heptylphenol is used in place of bisphenol A (yield: 95 %). From the results of infrared absorption spectrometry and mass spectrometry [m/e 292 (M + )], it is confirmed that the oil [S10] is a compound having the following structural formula: The kinetic viscosity of the oil [S10] at 40 °C is 3.1 cSt. Referential Example 11 (comparative) Comparative Oil [S11] is obtained in substantially the same manner as in Referential Example 1 except that nonylphenol is used in place of bisphenol A (yield: 92 %). From the results of infrared absorption spectrometry and mass spectrometry [m/e 320 (M + )], it is confirmed that the oil [S11] is a compound having the following structural formula: The kinetic viscosity of the oil [S11] at 40 °C is 6.2 cSt. Referential Example 12 (comparative) Comparative Oil [S12] is obtained in substantially the same manner as in Referential Example 1 except that dodecylphenol is used in place of bisphenol A (yield: 93 %). From the results of infrared absorption spectrometry and mass spectrometry [m/e 362 (M + )], it is confirmed that the oil [S12] is a compound having the following structural formula: The kinetic viscosity of the oil [S12] at 40 °C is 14 cSt. Referential Example 13 (present invention) Oil [S13] is obtained in substantially the same manner as in Referential Example 1 except that compound [G1] shown in Referential Example 3 is used in place of bisphenol A, that perfluoropropylvinyl ether (CF 2 =CFOCF 2 CF 2 CF 3 ) is used in place of tetrafluoroethyiene, and that the synthesis is conducted on a scale of 1/20 of that of Referential Example 1. Oil [S13] is isolated from the crude reaction product by means of Kugel Rohr type micro-distillation apparatus. From the results of infrared absorption spectrometry and mass spectrometry [m/e 802 (M + )], it is confirmed that the oil [S13] is a compound having the following structural formula: Referential Example 14 (present invention) Oil [S14] is obtained in substantially the same manner as in Referential Example 1 except that compound [G1] shown in Referential Example 3 is used in place of bisphenol A, that hexafluoropropene (CF 2 =CFCF 3 ) is used in place of tetrafluoroethylene, and that the synthesis is conducted in a scale of 1/20 that of Referential Example 1. Oil [S14] is isolated from the crude reaction product by means of Kugel Rohr type micro-distillation apparatus. From the results of infrared absorption spectrometry and mass spectrometry [m/e 530, 550, 570 (M + )], it is confirmed that the oil [S14] is a mixture of substances represented by the following structural formula: wherein R f a groups each independently represent CF 3 CF=CF- or CF 3 CHFCF 2 -. Referential Example 15 (comparative) <Miscibility Test between the compound (A) and various types of oils including the alkyl- or alkyl derivative-substituted aromatic compound (B)> The miscibility of the comparative compound [S1] [compound] (A)] obtained in Referential Example 1 with Aromix 20T [compound (B)] (tradename of (branched)alkylbenzene having a kinetic viscosity at 40 °C of 14 cSt, manufactured and sold by Nippon Petroleum Detergent Co., Ltd., Japan) is evaluated at 25 °C by the following method. 100 parts by weight of the compound [S1] is placed in a beaker, and Aromix 20T is stepwise added thereto 1 part by 1 part by weight until the total amount of added Aromix 20T becomes 100 parts by weight, while visually evaluating the miscibility of the compound [S1] with the Aromix 20T. Separately, 100 parts by weight of Aromix 20T is placed in a beaker, and the compound [S1] is stepwise added thereto 1 part by 1 part by weight 'until the total amount of added compound [S1] becomes 100 parts by weight, while visually evaluating the miscibility of the compound [S1] with the Aromix 20T. As a result, it is found that the compound [S1] is completely miscible with Aromix 20T over the entire weight ratio range. Results are shown in Table 1. Referential Examples 16 and 17 (comparative) Substantially the same procedure as in Referential Example 5 is repeated except that Aromix 22 [compound (B)] (tradename of (branched)alkylbenzene having a kinetic viscosity at 40 °C of 31.5 cSt, manufactured and sold by Nippon Petroleum Detergent Co., Ltd., Japan) and AB-SG [compound (B)] (tradename of (linear)alkylbenzene having a kinetic viscosity at 30 °C of 5.8 cSt, manufactured and sold by Mitsubishi Petrochemical Co., Ltd., Japan) are individually used (respectively in Referential Examples 16 and 17) in place of Aromix 20T, thereby evaluating the miscibility at 25 °C of the comparative compound [S1] with each of Aromix 22 and AB-SG. As a result, it is found that the compound [S1] is completely miscible with each of Aromix 22 and AB-SG over the entire weight ratio range. Results are shown in Table 1. Referential Examples 18 and 19 (comparative) Substantially the same procedure as in Referential Example 15 is repeated except that SUNISO 3GS [compound (B)] (tradename of a naphthene mineral oil having a kinetic viscosity at 40 °C of 30 cSt, manufactured and sold by Japan Sun Oil Company, Ltd., Japan) and a liquid paraffin [compound (B)] (having a kinetic viscosity at 40 °C of 40 cSt and which is a first grade reagent manufactured and sold by Wako Pure Chemical Industries, Ltd., Japan) are individually used (respectively in Referential Examples 18 and 19) in place of Aromix 20T, thereby evaluating the miscibility at 25 °C of the comparative compound [S1] with each of SUNISO 3GS and the liquid paraffin. As a result, it is found that the compound [S1] is miscible with each of SUNISO 3GS and the liquid paraffin only in a limited weight ratio range. Results are also shown in Table 1. In Tables 1 to 2, "Component I" and "Component II" are inserted in order to identify two components of each of the lubricant oil compositions used in Examples and Comparative Examples. That is, "Component I" is used to identify the fluorine-containing aromatic compound (A) or (C-1) for the lubricant oil composition, and other fluoro compound, such as perfluoropolyether, while "Component II" is used in order to identify the alkyl- or alkyl derivative-substituted aromatic compound (B) for the lubricant oil composition and a non-aromatic compound, such as ester oil. As is apparent from Referential Examples 15 to 19, the compound [S1], which falls within the class of the compound (A) is completely miscible with an aromatic hydrocarbon over the entire weight ratio range, and the compound [S1] is miscible with a non-aromatic compound only in a limited weight ratio range. Referential Example 20 (comparative) <Miscibility Test between the lubricant oil composition and HFC-134a> The comparative compound [S1] obtained in Referential Example 1 is mixed with Aromix 20T in a weight ratio ([S1]/Aromix 20T) of 80/20, to thereby obtain a lubricant oil composition. The miscibility of the obtained lubricant oil composition with 1,1,1,2-tetrafluoroethane (HFC-134a) as a refrigerant is evaluated by the following method. First, 1.8 g of the lubricant oil composition is charged in a glass tube having an internal volume of 6 ml and then, the whole is cooled by liquid nitrogen. The interior of the glass tube is evacuated and then, about 0.2 g of HFC-134a is introduced into the glass tube. The glass tube is sealed, and the miscibility of the lubricant oil composition with HFC-134a at room temperature is visually evaluated. Then, a lower limit temperature of the lubricant oil composition for being miscible with HFC-134a is measured as follows. The glass tube is cooled with a cooling medium composed of methanol and, after the temperature is equilibrated, the miscibility is visually evaluated. The temperature at which a clear, homogeneous liquid mixture of the lubricant oil composition and HFC-134a begins to become a turbid suspension, is taken as the lower limit temperature. Results of the test are shown in Table 2. Referential Examples 21 and 22 (comparative) A lubricant oil composition is prepared in substantially the same manner as in Referential Example 20 except that Alken L [compound (B)] (tradename of (linear)alkylbenzene having a kinetic viscosity at 40 °C of 4.3 cSt, manufactured and sold by Nippon Petroleum Detergent Co., Ltd., Japan) and AB-SG [compound (B)] (tradename of (linear)alkylbenzene having a kinetic viscosity at 40 °C of 5.8 cSt, manufactured and sold by Mitsubishi Petrochemical Co., Ltd., Japan) are individually used (in Referential Examples 21 and 22) in place of Aromix 20T. Then, in substantially the same manner as in Referential Example 20, the miscibility of the lubricant oil composition with HFC-134a is evaluated. Results are shown in Table 2. Referential Example 23 (comparative) Substantially the same procedure as in Referential Example 20 is repeated except that the comparative compound [S2] [compound (A)] obtained in Referential Example 2 is used in place of the comparative compound [S1], thereby evaluating the miscibility of the lubricant oil composition with HFC-134a. Results are shown in Table 2. Referential Example 24 Substantially the same procedure as in Referential Example 20 is repeated except that the comparative compound [S1] is mixed with Aromix 20T in a weight ratio ([Sl]/Aromix 20T) of 20/80, thereby evaluating the miscibility of the lubricant oil composition with HFC-134a. Results are shown in Table 2. Referential Examples 25 to 27 (comparative) Substantially the same procedure as in Referential Example 20 is repeated except that each of the comparative compound [S1] and the comparative compound [S2] is individually mixed with each of various non-aromatic compounds indicated in Table 2, thereby evaluating'the miscibility of the lubricant oil composition with HFC-134a. Results are shown in Table 2. As is apparent from Referential Examples 20 to 27, a lubricant oil composition comprising a compound (A) and an alkyl- or alkyl derivative-substituted aromatic compound (B) exhibits a good miscibility with HFC-134a even at low temperatures, as compared to the lubricant oil composition comprising the fluorine-containing aromatic compound (A) and a non-aromatic compound. Examples 1 to 5 Substantially the same procedure as in Referential Example 15 is repeated except that the compound [S3] [compound (C-1)] obtained in Referential Example 3 is mixed with individual alkyl- or alkyl derivative-substituted aromatic compounds ( B ) indicated in Table 3, thereby evaluating the miscibility at 25 °C of the compound [S3] with individual alkyl- or alkyl derivative-substituted aromatic compounds. Results are shown in Table 3. Example 6 Substantially the same procedure as in Referential Example 15 is repeated except that the compound [S3] is used in place of the comparative compound [S1] and a liquid paraffin (having a kinetic viscosity at 40 °C of 40 cSt and which is a first grade reagent manufactured and sold by Wako Pure Chemical Industries, Ltd., Japan) is used in place of Aromix 20T, thereby evaluating the miscibility at 25 °C of the compound [S3] with the liquid paraffin. Results are shown in Table 3. As is apparent from Examples 1 to 6, the compound [S3] [i.e. a fluorine-containing aromatic compound (A), particularly represented by formula (C-1)] is completely miscible with the alkyl- or alkyl derivative-substituted aromatic compound (B) over the entire weight ratio range, although the compound [S3] is miscible with a non-aromatic compound only in a limited weight ratio range. Examples 7 to 9 Lubricant oil compositions are individually prepared in accordance with the formulations indicated in Table 4, using the compound [S3] and each of various alkyl- or alkyl derivative-substituted aromatic compounds [compound (B)] indicated in Table 4. Then, in substantially the same manner as in Referential Example 20, the miscibility of each of the lubricant oil compositions with HFC-134a is evaluated. Results are shown in Table 4. Example 10 A lubricant oil composition is prepared by mixing the compound [S3] and SUNISO 3GS in a weight ratio ([S3]/SUNISO 3GS) of 80/20. Then, in substantially the same manner as in Referential Example 20, the miscibility of the lubricant oil composition with HFC-134a is evaluated. Results are shown in Table 4. As is apparent from Examples 7 to 10, the lubricant oil composition comprising the fluorine-containing aromatic compound (C-1), and the alkyl- or alkyl derivative-substituted aromatic compound (B) exhibits a good miscibility with HFC-134a even at low temperatures, as compared to the lubricant oil composition comprising the fluorine-containing aromatic compound (C-1) and the non-aromatic compound. Further, when Referential Examples 22 and 24 (in which the comparative compound [S1] is employed) are compared with Examples 8 and 9 [in which the compound [S3] (i.e., the compound of the present invention) is employed], it is found that the lubricant oil composition containing the compound [S3] exhibits a lower limit temperature for miscibility which is far lower than that of a lubricant oil composition containing the comparative compound [S1] as the compound (A), despite the fact that the former is more viscous than the latter. Examples 11 to 14 Lubricant oil compositions are individually prepared by mixing the compound [S3] and Aromix 20T in various weight ratios indicated in Table 5. Then, a miscibility test is conducted in substantially the same manner as in Referential Example 20, except that a mixed refrigerant of HFC-32/HFC-125/HFC-134a (weight ratio: 30/10/60) is used as the refrigerant in place of HFC-134a, to thereby evaluate the miscibility of each of the lubricant oil compositions with the mixed refrigerant of HFC-32/HFC-125/HFC-134a. Results are shown in Table 5. As is apparent from Examples 11 to 14, the lubricant oil compositions prepared by mixing the fluorine-containing aromatic compound (C-1) and the alkyl- or alkyl derivative-substituted aromatic compound (B) in various weight ratios exhibit a good miscibility with a mixed refrigerant of HFC-32/HFC-125/HFC-134a (weight ratio: 30/10/60) even at low temperatures. Examples 15 to 17 A lubricant oil composition is prepared by mixing the compound [S3] and Aromix 20T in a weight ratio ([S3]/Aromix 20T) of 80/20. Then, a miscibility test is conducted in substantially the same manner as in Referential Example 20, except that a mixed refrigerant of HFC-143a/HFC-134a/HFC-125 (weight ratio: 52/4/44) is used as the refrigerant in place of HFC-134a, and that the weight ratio of the lubricant oil composition to the refrigerant is varied as indicated in Table 6, thereby evaluating the miscibility of the lubricant oil composition with the mixed refrigerant of HFC-143a/HFC-134a/HFC-125. Results are shown in Table 6. Weight ratio of lubricant oil composition / mixed refrigerant Lower limit temperature for lubricant oil composition to be miscible with mixed refrigerant Example 15 70/30 -70 °C Example 16 40/60 -37 °C Example 17 5/95 -32 °c As is apparent from Examples 15 to 17, the lubricant oil composition comprising a fluorine-containing aromatic compound (C-1) and the alkyl- or alkyl derivative-substituted aromatic compound (B) exhibits a good miscibility with a mixed refrigerant of HFC-143a/HFC-134a/HFC-125 (weight ratio: 52/4/44) even at low temperatures, with respect to various mixing ratios of the lubricant oil composition to the mixed refrigerant. Example 18 A lubricant oil composition is prepared by mixing the compound [S3] and Aromix 20T in a weight ratio ([S3]/Aromix 20T) of 80/20. Then, a miscibility test is conducted in substantially the same manner as in Referential Example 20, except that a mixed refrigerant of HFC-32/HFC-125/HFC-134a (weight ratio: 23/25/52) is used as the refrigerant in place of HFC-134a, to thereby evaluate the miscibility of the lubricant oil composition with the mixed refrigerant of HFC-32/HFC-125/HFC-134a. It is found that the lubricant oil composition is miscible with the mixed refrigerant of HFC-32/HPC-125/HFC-134a at room temperature and the lower limit temperature for miscibility is -70 °C. Example 19 A lubricant oil composition is prepared by mixing the compound [S4] [compound (C-1)] obtained in Referential Example 4 and Aromix 20T in a weight' ratio ([S4]/Aromix 20T) of 80/20. Then, a miscibility test is conducted in substantially the same manner as in Referential Example 20, except that a mixed refrigerant of HFC-32/HFC-125/HFC-134a (weight ratio: 30/10/60) is used as the refrigerant in place of HFC-134a, to thereby evaluate the miscibility of the lubricant oil composition with the mixed refrigerant of HFC-32/HFC-125/HFC-134a. It is found that the lubricant oil composition is miscible with the mixed refrigerant of HFC-32/HFC-125/HFC-134a at room temperature, and also even at a temperature as low as -50 °C. Example 20 Alken 56N (trade name of (branched)alkylbenzene having a kinetic viscosity at 40 °C of 5.8 cSt, manufactured by Nippon Petroleum Detergent Co., Ltd.) and Aromix 22 (trade name of (branched)alkylbenzene having a kinetic viscosity at 40 °C of 29 cSt, manufactured by Nippon Petroleum Detergent Co., Ltd.) are mixed in a weight ratio (Alken 56N /Aromix 22) of 45/55, thereby obtaining an alkyl- or alkyl derivative-substituted compound (B) (having a kinetic viscosity at 40 °C of 14 cSt). Subsequently, the thus obtained compound (B) is mixed with the compound [S3] in a weight ratio ([S3]/the compound (B)) of 80/20, thereby preparing a lubricant oil composition. Then, a miscibility test is conducted in substantially the same manner as in Referential Example 20 except that the mixing ratio of the lubricant oil composition /HFC-134a is changed to 70/30 by weight ratio. It is found that the lubricant oil composition exhibits an excellent miscibility with HFC-134a at room temperature and that the lower limit temperature for miscibility is -50 °C. Examples 21 through 24 Miscibility tests are conducted in substantially the same manner as in Referential Example 20, except that a mixed refrigerant of HFC-32/HFC-125/HFC-134a (weight ratio: 30/10/60) is used as the refrigerant in place of HFC-134a, to thereby evaluate the miscibilities of the lubricant oil compositions comprising the compound [S3] and each of the alkyl- or alkyl derivative-substituted aromatic compound (B) shown in Table 7 with the mixed refrigerant of HFC-32/HFC-125/HFC-134a. Results are shown in Table 7. From the results shown in Table 7, it is apparent that each lubricant oil composition comprising a fluorine-containing aromatic compound (C-1) and (branched)alkylbenzene [compound (B)] exhibits an excellent miscibility with the mixed refrigerant of HFC-32/HFC-125/HFC-134a in a further low temperature range, as compared to a lubricant oil composition comprising (linear)alkylbenzene as compound (B). Example 25 A lubricant oil composition is prepared by mixing the compound [S3] with an alkyldiphenyl ether [compound (B)] (LB-15, having a kinetic viscosity at 40 °C of 15 cSt, manufactured by Matsumura Oil Research Co., Ltd.) in a weight ratio ([S3]/alkyldiphenyl ether) of 82/18-Then, a miscibility test is conducted by mixing the lubricant oil composition and HFC-134a in a weight ratio (the oil composition /HFC-134a) of 70/30 in substantially the same manner as in Referential Example 20, to thereby evaluate the miscibility of the lubricant oil composition with HFC-134a. It is found that the lubricant oil composition is miscible with HFC-134a at room temperature and that the lower limit temperature for miscibility is -42 °C. Examples 26 through 29, and Comparative Example 1. Each of the compounds [S1] and [S3] is individually mixed with each of various types of hydrofluoroether (HFE) refrigerants indicated in Table 8 in a weight ratio (the compound/the HFE refrigerant) of 10/90. The miscibilities of each of the compounds [S1] and [S3] with the various types of HFE refrigerants are evaluated in substantially the same manner as in Referential Example 20. Results are shown in Table 8. Comparative Examples 1a through 5 In each comparative example, a perfluoropolyether (Fomblin Y-06, having a kinetic viscosity at 40 °C of 27 cSt, manufactured by NIPPON MONTEDISON KK) or a mineral oil (SUNISO 3GS, manufactured by Japan Sun Oil Company, Ltd) is mixed with various types of HFE refrigerants in a weight ratio (the lubricant oil/the fluorine-containing ether) of 10/90. The miscibilities of each of the lubricant oils with the various types of HFE refrigerants are evaluated in substantially the same manner as in Referential Example 20. Results are shown in Table 8. From the results shown in Table 8, it is apparent that a perfluoropolyether and a mineral oil exhibit an unsatisfactory miscibility with HFE refrigerants, while fluorine-containing aromatic compounds (A) represented by formula (A) exhibit excellent miscibility with various types of HFE refrigerants. Examples 30 and 31 Lubricant oil compositions are individually prepared by mixing the compound [S3] with each of the alkyl- or alkyl derivative-substituted aromatic compounds (B) indicated in Table 9 in a weight ratio indicated in Table 9. Each of the obtained oil composition is individually mixed with each of various HFE refrigerants in a weight ratio (Lubricant oil/HFE refrigerant) of 70/30. The miscibility of each of the lubricant oil compositions with each of the HFE refrigerants is evaluated in substantially the same manner as in Referential Example 20. Results are shown in Table 9. Comparative Examples 6 and 7 Each of a perfluoropolyether (Fomblin Y-06, having a kinetic viscosity at 40 °C of 27 cSt, manufactured by NIPPON MONTEDISON KK) and a mineral oil (SUNISO 3GS, manufactured by JAPAN SUN OIL COMPANY, Ltd) is individually mixed with each of various HFE refrigerants in a weight ratio (lubricant oil/HFE refrigerant) of 70/30. Then the miscibility of each of the lubricant oils with each of the various types of HFE refrigerants are evaluated in substantially the same manner as in Referential Example 20. Results are shown in Table 9. From the results shown in Table 9, it is apparent that a perfluoropolyether and a mineral oil exhibit an unsatisfactory miscibility with HFE refrigerants, while lubricant oil compositions comprising-the fluorine-containing aromatic compound (C-1) and the alkyl- or alkyl derivative-substituted aromatic compound (B) exhibit excellent miscibility with various HFE refrigerants even in a lower temperature range. Examples 32 through 35. <Pour Point Test> With respect to the lubricant oil compound [S3] alone and the lubricant oil compositions shown in Table 10, the pour points are measured according to the method of JIS K2269-1987 (pour point test). Results are shown in Table 10. Example Component I: Compound (C-1) Component II: Compound (B) Weight ratio of (I)/(II) Pour point 32 [S3] - - -15 °C 33 [S3] Aromix 20T 50/50 -35 °C 34 [S3] Aromix 22 50/50 -33 °C 35 [S3] AB-SG 50/50 -60 °C From the results of Table 10, it is apparent that the fluidity at low temperatures is markedly improved by mixing the fluorine-containing aromatic compound (C-1) with the alkyl- or alkyl derivative-substituted aromatic compound (B). Examples 36 through 39 <Water Absorption Test> The lubricant oil compound [S3] alone or the lubricant oil compositions individually comprised of the compound [S3] and each of the various alkyl- or alkyl derivative-substituted aromatic compounds shown in Table 11 are individually allowed to stand in a thermo-hygrostat vessel maintained at a temperature of 25 °C and at a relative humidity of 70 %, and the equilibrium water absorptions thereof are measured, by means of Karl Fischer moisture meter. Results are shown in Table 11. Example 40 The equilibrium water absorption of a lubricant oil composition comprised of the compound [S3] and an ester oil (pentaerythritol fatty acid ester having a kinetic viscosity of 32 cSt at 40 °C) is measured in the same manner as described in Example 36. Result is shown in Table 11. Component I: Compound (C-1) Component II: Compound (B) or non-aromatic compound Weight ratio of (I)/(II) Equilibrium water absorption (ppm) Ex. 36 [S3] - - 250 Ex. 37 [S3] Aromix 20T 50/50 140 Ex. 38 [S3] Aromix 22 50/50 130 Ex. 39 [S3] Aromix loop 50/50 110 Ex. 40 [S3] ester oil 50/50 430 Table 11 clearly shows that the water absorption is markedly lowered when the fluorine-containing aromatic compound (C-1) is mixed with the alkyl or alkyl derivative-substituted aromatic compound (B). Comparative Example 8 The equilibrium water absorption of an ester oil (pentaerythritol fatty acid ester having a kinetic viscosity of 32 cSt at 40 °C) is measured in the same manner as described in Example 36. As a result, it was 'found that the ester oil had an equilibrium water absorption of 1300 as measured at 25 °C and at a relative humidity of 80 %. Therefore, it is apparent that the ester oil has very high water absorbing properties, as compared to the lubricant oil compositions obtained in Examples 36 to 40, each of which contains the compound (C-1) of the present invention. Examples 41 through 43 <Electrical Properties> The volume resistivities of the lubricant oil [S3] and the lubricant oil compositions individually comprised of the oil [S3] and each of the alkyl- or alkyl derivative-substituted aromatic compounds shown in Table 12 are individually measured according to the method of JIS C2101 (insulating oil test). Results are shown in Table 12. Component I: Compound (C-1) Component II: Compound (B) Weight ratio of (I)/(II) Volume resistivity (Ωcm) before water absorption after water absorption Ex. 41 [S3] - - 2.0 x 10 13 1.0 x 10 12 Ex. 42 [S3] Aromix 20T 80/20 2.1 x 10 13 1.0 x 10 13 Ex. 43 [S3] Aromix 22 50/50 1.1 x 10 14 5.0 x 10 13 Table 12 clearly shows that the decrease in volume resistivity of each of the lubricant oil compositions due to the water absorption is less than that of the oil alone. Example 44. <Bioconcentration Test> The test is conducted substantially in accordance with <Method for Testing the Degree of Bioconcentration of Chemical Substances in Fishes> promulgated in "Test Relating to the New Chemical Substance" (Japanese Environment Agency Notification, No. KANPOGYO 5, Japanese Ministry of Health and Welfare Notification, No. YAKUHATSU 615, and Japanese Ministry of International Trade and Industry 49 KIKYOKU Notification No. 392, July 13, 1974) and <Bioaccumulation: Degree of Bioconcentration in Fish> promulgated in "OECD Guidelines for Testing of Chemicals, 305C" (May 12, 1981). The illustrative procedure of the test is described below in detail. The compound [S3] is dissolved in water to prepare a test solution having a compound [S3] concentration of 0.01 mg/liter. Normal carps, after acclimatization, are subjected to exposure test in the test solution. After 2-week and 4-week exposures, the carps are collected. The fishes are minced, homogenized and subjected to centrifugation. After the centrifugation, the degree of bioconcentration of the compound [S3], which is defined as a ratio of the concentration of the compound [S3] in a fish body to that of the test solution, is measured by high performance liquid chromatography. Results are shown in Table 13. Comparative Examples 8 and 9 The degrees of bioconcentration are measured also with respect to the comparative compound [S7] obtained in Referential Example 7 and the comparative compound [SI] obtained in Referential Example 1, in the same manner as described in Example 44. Results are shown in Table 13. Fluorine-containing aromatic Compound (A) or (C-1) Degree of bioconcentration after 2 weeks after 4 weeks Ex. 44 [S3] 303 583 Comp. Ex. 8 [S9] 3990 9240 Comp. Ex. 9 [S1] 4400 11900 Table 13 clearly shows that the degree of bioconcentration of the compound (C-1) is especially low among the compounds (A). Examples 45 and 46 <Heat Resistance> The fluorine-containing aromatic compounds [S3] and [S5] [compound (C-1)] obtained in Referential Example 6 are evaluated with respect to the heat resistance by a method described below. A glass tube is charged with 0.5 ml of each of the compound [S3] and the compound [S5], individually. Each of the compounds is individually heated and kept at a temperature of 175 °C for 19 hours under air. The obtained substance is analyzed by gas chromatography to examine if the compound is thermally decomposed. Results are shown in Table 14. Comparative Examples 10 and 11 The comparative compound [S8] and [S9] obtained, respectively, in Referential Examples 8 and 9 are evaluated with respect to the heat resistance by the same method as described in Example 45. Results are shown in Table 14. Fluorine-containing aromatic compound (A) or (C-1) Degree of thermal decomposition Ex. 45 [S3] less than 0.01 % Ex. 46 [S5] 0.2 % Comp. Ex. 10 [S8] 10 % Comp. Ex. 11 [S9] 20 % Table 14 clearly shows that, among the compounds represented by formula (A), the compounds of formula (C-1) exhibit especially high heat resistance. Comparative Examples 12 through 14 The comparative compounds [S10], [S11] and [S12] obtained, respectively, in Referential Examples 10, 11 and 12 are evaluated with respect to the heat resistance by the same method as described in Example 45. Results are shown in Table 15. [The comparative compounds [S11] and [S12] are derivatives of an alkylphenol derivative synthesized from a propylene oligomer. The structures of the alkyl groups bonded to an aromatic nucleus are of the mixture of secondary alkyl and tertiary alkyl structures.] Fluorine-containing aromatic compound (A) Degree of thermal degradation Comp. Ex. 12 [S10] 15 % Comp. Ex. 13 [S11] 4 % Comp. Ex. 14 [S12] 3 % Table 15 clearly shows that the compounds (A) other than compound (C-1) have low heat resistance properties, as compared to the compound (C-1). Examples 47 and 48 <Lubrication Test (Falex Test)> Lubrication tests are conducted with respect to the lubricant oil [S3] and the lubricant oil compositions indicated in Table 16 under conditions described below. Use is made of a Falex tester. First, a refrigerant gas (HFC-134a) is blown into a sample (oil or an oil composition) at a blow rate of about 10 liter/hour for about 15 minutes. Further, under conditions such that the oil temperature at the start of the testing is 25 °C and a load of 200 pounds is applied, the Falex tester is driven for 5 minutes while continuing the gas blowing. The load is increased to 500 pounds, and the tester is driven for 2 hours while maintaining the load at 500 pounds by means of a gear. The weight of V-block and pin (test specimen) is measured before and after the test run, and the weight difference before and after the test run is defined as "wear (mg)". Results are shown in Table 16. Examples 49 through 53 The lubricant oil [S3] and the lubricant oil compositions indicated in Table 16 are individually mixed with each of various types of additives also indicated in Table 16, and the resultant mixtures are measured with respect to the weight loss of V-block and pin in the same manner as described in Example 47. Results are shown in Table 16. Comparative Examples 15 and 16 The abrasion losses of aromatic compounds containing no fluorine, including Aromix 20T and SUNISO3GS, are measured in the same manner as described in Example 47. Results are shown in Table 16. As is apparent from Table 16, the lubricant oil compositions each comprised of the fluorine-containing aromatic compound (C-1) and the alkyl- or alkyl derivative-substituted aromatic compound (B) have excellent abrasion resistance properties, as compared to the alkyl- or alkyl derivative-substituted aromatic compounds (B) alone as well as the fluorine-containing aromatic compounds (A) alone. Examples 53 through 56 <Resistance to Hydrolysis> Each of the fluorine-containing lubricant oils and the each of the fluorine-containing oil compositions indicated in Table 17 is individually allowed to absorb water to equilibrium in the same manner as described in Example 36. A glass tube is charged with 0.6 ml of each of the oils and the oil compositions, 0.6 ml of HFC-134a as liquid, 2 ml of air as gas, and a metal piece selected from steel, copper and aluminum. The glass tube is then sealed to enclose a refrigerant composition therein. The refrigerant composition is heated at 175 °C for 10 days. After the heating, any change in the hue of the refrigerant composition and any change in the surfaces of the metal piece are examined. It is found that both the hue of the refrigerant composition of the present invention and the surface of the metal are not changed. After evaluation, the oils and the oil compositions are analyzed by gas chromatography/mass spectrometry (GC/MASS). No decomposition is detected with respect to each of the fluorine-containing oils and with respect to each of the fluorine-containing oil compositions of the present invention. Further, the color change of the copper surface, which is slightly observed with respect to the lubricant oil alone, is not observed with respect to the fluorine-containing oil composition, i.e., the mixture of the fluorine-containing lubricant oil and the aromatic compound (B). Results are shown in Table 17. Comparative Example 17 Ester oil (pentaerythritol fatty acid ester having a kinetic viscosity of 32 cSt at 40 °C) is allowed to absorb water to equilibrium in the same manner as described in Comparative Example 8. The'obtained ester oil is evaluated with respect to the heat resistance and hydrolysis resistance in the same manner as described in Example 53. In the ester oil evaluated, decomposition products are detected. Results are shown in Table 17. As is apparent from Table 17, the refrigerant compositions using compound (C-1) alone as well as the refrigerant compositions using the lubricant oil composition composed of both of compound (C-1) and compound (B), exhibit satisfactory heat resistance and hydrolysis resistance. Examples 56 through 58 Each of the lubricant oil compositions indicated in Table 18 are evaluated with respect to the resistance to hydrolysis in the same manner as described in Example 61, except the temperature is elevated from 175 °C to 200 °C and the heating duration is prolonged from 10 days to 14 days so as to render the test conditions harder. Results are shown in Table 18. From Table 18, it is understood that anti-corrosives, such as benzotriazole and 2-ethylhexyl glycidyl ether, are effective to inhibit the color change of the surface of the metal piece. Example 59 <Miscibility Test between compound (C-1) and HFC-134a> The compound [S13] [compound (C-1)] obtained in Referential Example 13 is evaluated with respect to the miscibility with HFC-134a as a refrigerant by the following method. First, 1.8 g of oil compound [S13] is charged in a glass tube having an inner volume of 6 ml and then, the whole is cooled using liquid nitrogen. The interior of the glass tube is evacuated and, about 0.2 g of HFC-134a is introduced into the glass tube. The glass tube is sealed, and the miscibility of the oil compound [S13] with HFC-134a at 0 °C is visually evaluated. It is found that the compound [S13] is completely miscible with HFC-134a to form a homogeneous refrigerant composition. Example 60 Substantially the same procedure as in Example 59 is repeated except that the compound [S14] obtained in Referential Example 14 is used instead of the compound [S13], thereby evaluating the miscibility of the oil compound with HFC-134a at 0 °C. It is found that the oil compound is completely miscible with HFC-134a to form homogeneous refrigerant composition. Example 61 <Miscibility Test between a lubricant oil composition and HFC-134a> The compound [S13] is mixed with ethylbenzene in a weight ratio ([S13]/ethylbenzene) of 80/20, to thereby obtain a lubricant oil composition. The miscibility of the obtained lubricant oil composition with HFC-134a is evaluated in the same manner as described in Example 59. It is found that the oil composition is completely miscible with HFC-134a to form a homogeneous refrigerant composition. Examples 62 Substantially the same procedure as in Example 61 is repeated except that each of the lubricant oil compositions respectively containing compound [S14] [compound (C-1)] obtained in Referential Examples 14 instead of the compound [S13] is used, thereby evaluating the miscibility of the lubricant oil composition with HFC-134a at 0 °C. It is found that the lubricant oil composition is completely miscible with HFC-134a to form homogeneous refrigeous refrigerant composition. Example 63 The compound [S3] is mixed with a compound [E1] represented by the formula indicated below (having a kinetic viscosity of 18 cSt at 40 °C), in a weight ratio ([S3]/[E1]) of 80/20, to thereby obtain a lubricant oil composition (having a kinetic viscosity of 59 cSt at 40 °C). The miscibility of the oil composition with a mixed refrigerant of HFC-134a is evaluated in the same manner as in Referential Example 20, except that a mixed refrigerant of HFC-32/HFC-125/HFC-134a (mixed in a weight ratio of 30/10/60) is used as a hydrofluoroalkane in place of HFC-134a. The oil composition is mixed with the mixed refrigerant in a weight ratio of 70/30. It is found that the oil composition is miscible with the refrigerant at room temperature and also at -30 °C to form a homogeneous composition. Example 64 The compound [S3] is mixed with a compound [E2] represented by the formula indicated below (having a kinetic viscosity of 46 cSt at 40 °C), in a weight ratio ([S3]/[E2]) of 80/20, to thereby obtain a lubricant oil composition (having a kinetic viscosity of 80 cSt at 40 °C). The miscibility of the oil composition with a mixed refrigerant of HFC-32/HFC-125/HFC-134a is evaluated in the same manner as in Referential Example 20, except that a mixed refrigerant of HFC-32/HFC-125/HFC-134a (mixed in a weight ratio of 30/10/60) is used as a HFC refrigerant in place of HFC-134a. The oil composition is mixed with the mixed refrigerant in a weight ratio of 70/30. It is found that the oil composition is miscible with the HFC refrigerant at room temperature and also at -30 °C to form a homogeneous composition. Comparative Examples 18 through 22 <Miscibility Test between perfrluoropolyether and compound (B)> The miscibility of each of the various perfluoropolyethers indicated in Table 19 with Aromix 20T at 25 °C is individually evaluated in the same manner as described in Referential Example 15. It is found that those perfluoropolyethers are not miscible with Aromix 20T when they are mixed in a weight ratio of 80/20, 50/50 or 20/80 (perfluoropolyether/Aromix 20T).

Claims: A fluorine-containing aromatic compound represented by the formula: wherein: each of R 1 and R 2 independently represents a hydrogen atom or an alkyl group having from 1 to 19 carbon atoms, wherein the total number of carbon atoms in R 1 and R 2 is from 4 to 19; and each R f is an unsubstituted or partially substituted fluorocarbon group having from 1 to 25 carbon atoms in which the ratio of fluorine atom or atoms to carbon atom or atoms is from 0.6 to 3, wherein said unsubstituted fluorocarbon group is selected from the group consisting of a fluoroalkyl group, a fluoroalkenyl group, a fluoroaryl group, a fluoroalkylaryl and a fluoroaralkyl group, in which each of the alkyl, alkenyl, aryl, alkylaryl and aralkyl groups is partially or entirely substituted with at least one fluorine atom, and said partially substituted fluorocarbon group has at least one substituent other than fluorine and hydrogen atoms in an amount such that the ratio of said at least one substituent to the total number of fluorine and hydrogen atoms of said partially substituted fluorocarbon group is not greater than 1.5, and wherein a main chain of said unsubstituted or partially substituted fluorocarbon group optionally has from 1 to 7 ether linkages; wherein the R f groups are the same or different. The fluorine-containing aromatic compound according to claim 1, wherein said R f is selected from the group consisting of a fluoroalkyl and a fluoroalkenyl group each having from 1 to 10 carbon atoms. The fluorine-containing aromatic compound according to claim 1, wherein said R f is a fluoroalkyl group having from 2 to 25 carbon atoms and having in a main chain thereof 1 to 7 ether linkages. The fluorine-containing aromatic compound according to claim 1, wherein said R f is substituted with from 1 to 4 chlorine atoms. The fluorine-containing aromatic compound according to claim 1, wherein said R f is selected from the group consisting of an unsubstituted fluoroalkyl group having from 1 to 3 carbon atoms, -CF=CFCF 3 , -CF 2 CFClH, -CF=CFCl, and wherein n is an integer of from 0 to 6.

Inventors: FUKUI HIROYUKI, IKEDA MASANORI, SANECHIKA KENICHI, FUKUI, HIROYUKI, IKEDA, MASANORI, SANECHIKA, KENICHI, Sanechika, Kenichi 1-31, Asahi Kasei Mitsukyo Shat
Applicants: ASAHI CHEMICAL IND, ASAHI KASEI KABUSHIKI KAISHA
Application year: 1994
Main classification: C10M105
IPC codes: C10M171, C10M105